Error in loading the Arabic Billion Words Corpus
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I modified the dataset loading script to catch the `IndexError` and inspect the records at which the error is happening, and I found this:
For the `Techreen` config, the error happens in 36 records when trying to find the `Text` or `Dateline` tags. All these 36 records look something like:
```
<Techreen>
 <ID>TRN_ARB_0248167</ID>
 <URL>http://tishreen.news.sy/tishreen/public/read/248240</URL>
 <Headline>Removed, because the original articles was in English</Headline>
</Techreen>
```

and all the 288 faulty records in the `Almustaqbal` config look like:
```
<Almustaqbal>
 <ID>MTL_ARB_0028398</ID>
 
 <URL>http://www.almustaqbal.com/v4/article.aspx?type=NP&ArticleID=179015</URL>
 <Headline> Removed because it is not available in the original site</Headline>
</Almustaqbal>
```

so the error is happening because the articles were removed and so the associated records lack the `Text` tag.

In this case, I think we just need to catch the `IndexError` and ignore (pass) it.
 Thanks @M-Salti for reporting this issue and for your investigation.

Indeed, those `IndexError` should be catched and the corresponding record should be ignored.

I'm opening a Pull Request to fix it.
## Describe the bug
I get `IndexError: list index out of range` when trying to load the `Techreen` and `Almustaqbal` configs of the dataset.

## Steps to reproduce the bug
```python
load_dataset("arabic_billion_words", "Techreen")
load_dataset("arabic_billion_words", "Almustaqbal")
```

## Expected results
The datasets load succefully.

## Actual results
```python
_extract_tags(self, sample, tag)
    139             if len(out) > 0:
    140                 break
--> 141         return out[0]
    142 
    143     def _clean_text(self, text):

IndexError: list index out of range
```

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 1.10.2
- Platform: Ubuntu 18.04.5 LTS
- Python version: 3.7.11
- PyArrow version: 3.0.0

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