Bugfix for the wiki_reader

[oroszgy]

Bugfix for reading Wikipedia dumps

Description

Using wiki_reader.py for parsing the Hungarian wikipedia throws an error.

Motivation and Context

Parsing the Hungarian dump throws this error:

  File "./corpus-utils/wiki2txt.py", line 76, in <module>
    plac.call(main)
  File "/home/gorosz/miniconda3/envs/spacy-dev/lib/python2.7/site-packages/plac_core.py", line 328, in call
    cmd, result = parser.consume(arglist)
  File "/home/gorosz/miniconda3/envs/spacy-dev/lib/python2.7/site-packages/plac_core.py", line 207, in consume
    return cmd, self.func(*(args + varargs + extraopts), **kwargs)
  File "./corpus-utils/wiki2txt.py", line 66, in main
    for id, title, content in tqdm(reader):
  File "/home/gorosz/miniconda3/envs/spacy-dev/lib/python2.7/site-packages/tqdm/_tqdm.py", line 833, in __iter__
    for obj in iterable:
  File "/home/gorosz/miniconda3/envs/spacy-dev/lib/python2.7/site-packages/textacy/corpora/wiki_reader.py", line 158, in __iter__
    content = bytes_to_unicode(content, errors='ignore')
  File "/home/gorosz/miniconda3/envs/spacy-dev/lib/python2.7/site-packages/textacy/compat.py", line 17, in bytes_to_unicode
    return unicode_type(b, encoding=encoding, errors=errors)
TypeError: coercing to Unicode: need string or buffer, NoneType found

How Has This Been Tested?

Now it can parse the huwiki dump.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation, and I have updated it accordingly.

[bdewilde]

Hey @oroszgy , thanks a ton for the PR! Your changes look good to me.