ImageMagick 7.0.8-50 Q16 has a heap-based buffer over-read at MagickCore/threshold.c in AdaptiveThresholdImage because a width of zero is mishandled.
### Prerequisites

- [x] I have written a descriptive issue title
- [x] I have verified that I am using the latest version of ImageMagick
- [x] I have searched [open](https://github.com/ImageMagick/ImageMagick/issues) and [closed](https://github.com/ImageMagick/ImageMagick/issues?q=is%3Aissue+is%3Aclosed) issues to ensure it has not already been reported

### Description
<!-- A description of the bug or feature -->
There's a heap-buffer-overflow at MagickCore/threshold.c:323:33 in AdaptiveThresholdImage

### Steps to Reproduce
<!-- List of steps, sample code, failing test or link to a project that reproduces the behavior.
     Make sure you place a stack trace inside a code (```) block to avoid linking unrelated issues -->
run_cmd:
`magick -seed 0 "(" magick:logo +repage ")" "(" magick:wizard -lat 0x564-42%  ")" -quiet   tmp`

Here's ASAN log.
```
==10393==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7f8ba61737f0 at pc 0x7f8bb5c0f9fa bp 0x7ffc04d5fad0 sp 0x7ffc04d5fac8
READ of size 4 at 0x7f8ba61737f0 thread T0
    #0 0x7f8bb5c0f9f9 in AdaptiveThresholdImage MagickCore/threshold.c:323:33
    #1 0x7f8bb51c1cb6 in CLISimpleOperatorImage MagickWand/operation.c:2571:21
    #2 0x7f8bb51b6c78 in CLISimpleOperatorImages MagickWand/operation.c:3685:12
    #3 0x7f8bb51dc315 in CLIOption MagickWand/operation.c:5273:16
    #4 0x7f8bb501da99 in ProcessCommandOptions MagickWand/magick-cli.c:477:7
    #5 0x7f8bb501ed0a in MagickImageCommand MagickWand/magick-cli.c:796:5
    #6 0x7f8bb5068ba1 in MagickCommandGenesis MagickWand/mogrify.c:185:14
    #7 0x526f95 in MagickMain utilities/magick.c:149:10
    #8 0x5268e1 in main utilities/magick.c:180:10
    #9 0x7f8bafadfb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #10 0x41b069 in _start (install/bin/magick+0x41b069)

0x7f8ba61737f0 is located 16 bytes to the left of 4331520-byte region [0x7f8ba6173800,0x7f8ba6595000)
allocated by thread T0 here:
    #0 0x4e6200 in __interceptor_posix_memalign (install/bin/magick+0x4e6200)
    #1 0x7f8bb5a57ed6 in AcquireAlignedMemory MagickCore/memory.c:265:7
    #2 0x7f8bb57aeccc in AcquireCacheNexusPixels MagickCore/cache.c:4968:37
    #3 0x7f8bb579c13b in SetPixelCacheNexusPixels MagickCore/cache.c:5070:12
    #4 0x7f8bb5793b05 in GetVirtualPixelCacheNexus MagickCore/cache.c:2751:10
    #5 0x7f8bb57b1ea6 in GetCacheViewVirtualPixels MagickCore/cache-view.c:664:10
    #6 0x7f8bb5c0ef20 in AdaptiveThresholdImage MagickCore/threshold.c:257:7
    #7 0x7f8bb51c1cb6 in CLISimpleOperatorImage MagickWand/operation.c:2571:21
    #8 0x7f8bb51b6c78 in CLISimpleOperatorImages MagickWand/operation.c:3685:12
    #9 0x7f8bb51dc315 in CLIOption MagickWand/operation.c:5273:16
    #10 0x7f8bb501da99 in ProcessCommandOptions MagickWand/magick-cli.c:477:7
    #11 0x7f8bb501ed0a in MagickImageCommand MagickWand/magick-cli.c:796:5
    #12 0x7f8bb5068ba1 in MagickCommandGenesis MagickWand/mogrify.c:185:14
    #13 0x526f95 in MagickMain utilities/magick.c:149:10
    #14 0x5268e1 in main utilities/magick.c:180:10
    #15 0x7f8bafadfb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)

SUMMARY: AddressSanitizer: heap-buffer-overflow MagickCore/threshold.c:323:33 in AdaptiveThresholdImage
```

### System Configuration
<!-- Tell us about the environment where you are experiencing the bug -->

- ImageMagick version:
Version: ImageMagick 7.0.8-50 Q16 x86_64 2019-06-21 https://imagemagick.org

- Environment (Operating system, version and so on):
Description:	Ubuntu 18.04.1 LTS
Release:	18.04
Codename: bionic

- Additional information:
CC=clang-7 CXX=clang++-7 ./configure --disable-openmp
<!-- Thanks for reporting the issue to ImageMagick! -->

heap-buffer-overflow at MagickCore/threshold.c:323:33 in AdaptiveThresholdImage
This is a GitHub Issue
repo:ImageMagick
owner:ImageMagick
Title : heap-buffer-overflow at MagickCore/threshold.c:323:33 in AdaptiveThresholdImage
Issue date:

--- start body ---
### Prerequisites

- [x] I have written a descriptive issue title
- [x] I have verified that I am using the latest version of ImageMagick
- [x] I have searched [open](https://github.com/ImageMagick/ImageMagick/issues) and [closed](https://github.com/ImageMagick/ImageMagick/issues?q=is%3Aissue+is%3Aclosed) issues to ensure it has not already been reported

### Description
<!-- A description of the bug or feature -->
There's a heap-buffer-overflow at MagickCore/threshold.c:323:33 in AdaptiveThresholdImage

### Steps to Reproduce
<!-- List of steps, sample code, failing test or link to a project that reproduces the behavior.
     Make sure you place a stack trace inside a code (```) block to avoid linking unrelated issues -->
run_cmd:
`magick -seed 0 "(" magick:logo +repage ")" "(" magick:wizard -lat 0x564-42%  ")" -quiet   tmp`

Here's ASAN log.
```
==10393==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7f8ba61737f0 at pc 0x7f8bb5c0f9fa bp 0x7ffc04d5fad0 sp 0x7ffc04d5fac8
READ of size 4 at 0x7f8ba61737f0 thread T0
    #0 0x7f8bb5c0f9f9 in AdaptiveThresholdImage MagickCore/threshold.c:323:33
    #1 0x7f8bb51c1cb6 in CLISimpleOperatorImage MagickWand/operation.c:2571:21
    #2 0x7f8bb51b6c78 in CLISimpleOperatorImages MagickWand/operation.c:3685:12
    #3 0x7f8bb51dc315 in CLIOption MagickWand/operation.c:5273:16
    #4 0x7f8bb501da99 in ProcessCommandOptions MagickWand/magick-cli.c:477:7
    #5 0x7f8bb501ed0a in MagickImageCommand MagickWand/magick-cli.c:796:5
    #6 0x7f8bb5068ba1 in MagickCommandGenesis MagickWand/mogrify.c:185:14
    #7 0x526f95 in MagickMain utilities/magick.c:149:10
    #8 0x5268e1 in main utilities/magick.c:180:10
    #9 0x7f8bafadfb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #10 0x41b069 in _start (install/bin/magick+0x41b069)

0x7f8ba61737f0 is located 16 bytes to the left of 4331520-byte region [0x7f8ba6173800,0x7f8ba6595000)
allocated by thread T0 here:
    #0 0x4e6200 in __interceptor_posix_memalign (install/bin/magick+0x4e6200)
    #1 0x7f8bb5a57ed6 in AcquireAlignedMemory MagickCore/memory.c:265:7
    #2 0x7f8bb57aeccc in AcquireCacheNexusPixels MagickCore/cache.c:4968:37
    #3 0x7f8bb579c13b in SetPixelCacheNexusPixels MagickCore/cache.c:5070:12
    #4 0x7f8bb5793b05 in GetVirtualPixelCacheNexus MagickCore/cache.c:2751:10
    #5 0x7f8bb57b1ea6 in GetCacheViewVirtualPixels MagickCore/cache-view.c:664:10
    #6 0x7f8bb5c0ef20 in AdaptiveThresholdImage MagickCore/threshold.c:257:7
    #7 0x7f8bb51c1cb6 in CLISimpleOperatorImage MagickWand/operation.c:2571:21
    #8 0x7f8bb51b6c78 in CLISimpleOperatorImages MagickWand/operation.c:3685:12
    #9 0x7f8bb51dc315 in CLIOption MagickWand/operation.c:5273:16
    #10 0x7f8bb501da99 in ProcessCommandOptions MagickWand/magick-cli.c:477:7
    #11 0x7f8bb501ed0a in MagickImageCommand MagickWand/magick-cli.c:796:5
    #12 0x7f8bb5068ba1 in MagickCommandGenesis MagickWand/mogrify.c:185:14
    #13 0x526f95 in MagickMain utilities/magick.c:149:10
    #14 0x5268e1 in main utilities/magick.c:180:10
    #15 0x7f8bafadfb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)

SUMMARY: AddressSanitizer: heap-buffer-overflow MagickCore/threshold.c:323:33 in AdaptiveThresholdImage
```

### System Configuration
<!-- Tell us about the environment where you are experiencing the bug -->

- ImageMagick version:
Version: ImageMagick 7.0.8-50 Q16 x86_64 2019-06-21 https://imagemagick.org

- Environment (Operating system, version and so on):
Description:	Ubuntu 18.04.1 LTS
Release:	18.04
Codename: bionic

- Additional information:
CC=clang-7 CXX=clang++-7 ./configure --disable-openmp
<!-- Thanks for reporting the issue to ImageMagick! -->

--- end body ---

A heap-buffer-overflow vulnerability in the AdaptiveThresholdImage function of ImageMagick version 7.0.8-50 can be exploited by providing specially crafted input, leading to potential memory corruption and application crashes.