Fix of list index out of range error in PoFileParser.add_message when translations is empty

[gabe-sherman]

Addresses https://github.com/python-babel/babel/issues/1134

Previously, the add_message function would try to access the PoFileParser object's translations list without any checks. However, when an invalid po file is provided, this can lead to an index out of range error.

This PR adds a check to the _finish_current_message function and raises an invalid_pofile exception when the messages list is populated and translations is empty. This also adds a dummy translation to the translations list to avoid the index out of range error when an invalid_pofile exception is treated as a warning rather than raised.

[gabe-sherman]

I updated the error message and added a test. Let me know if there's any other changes that should be made!

[tomasr8]

Thanks! I'll take a look later today or tomorrow (ping me in case I forget)

[gabe-sherman]

Sorry for the delay, it's been a busy couple of days. I just added a couple more test cases!

[gabe-sherman]

Made those extra changes. Thanks for sticking with me as I work through everything!

[tomasr8]

Made those extra changes. Thanks for sticking with me as I work through everything!

Thank you for working on the fix! It's looking good to me but I don't have commit rights in this repo so I'm pinging @akx :slightly_smiling_face:

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.31%. Comparing base (f91754b) to head (2d72d66). Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1135      +/-   ##
==========================================
+ Coverage   91.26%   91.31%   +0.05%     
==========================================
  Files          27       27              
  Lines        4602     4618      +16     
==========================================
+ Hits         4200     4217      +17     
+ Misses        402      401       -1     

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[akx]

Thank you! The test was a bit buggy, so I went ahead and fixed that – and also that we don't do (a tiny bit of) extra work if we'd end up raising an error next anyway.