[image dialog] NoneType' object has no attribute 'index'
Occurred on `pyFAI-integrate` at the program termination. The dialog was closed a long time ago.

```
Traceback (most recent call last):
  File "/home/valls/.local/lib/python3.5/site-packages/silx/gui/dialog/AbstractDataFileDialog.py", line 1058, in __directoryLoaded
    index = self.__fileModel.index(path)
AttributeError: 'NoneType' object has no attribute 'index'
```
diff --git a/silx/gui/dialog/AbstractDataFileDialog.py b/silx/gui/dialog/AbstractDataFileDialog.py
index e79519d34..29e7bb563 100644
--- a/silx/gui/dialog/AbstractDataFileDialog.py
+++ b/silx/gui/dialog/AbstractDataFileDialog.py
@@ -1042,6 +1042,8 @@ class AbstractDataFileDialog(qt.QDialog):
                 return
         self.__directoryLoadedFilter = path
         self.__processing += 1
+        if self.__fileModel is None:
+            return
         index = self.__fileModel.setRootPath(path)
         if not index.isValid():
             # There is a problem with this path
@@ -1058,6 +1060,8 @@ class AbstractDataFileDialog(qt.QDialog):
                 # The first click on the sidebar sent 2 events
                 self.__processing -= 1
                 return
+        if self.__fileModel is None:
+            return
         index = self.__fileModel.index(path)
         self.__browser.setRootIndex(index, model=self.__fileModel)
         self.__updatePath()
['silx/gui/dialog/AbstractDataFileDialog.py']