Handle empty TranslationInfo tag properly when parsing Settings.xml

[pmachapman]

Fixes #401.

I tested by modifying the Settings.xml file manually. If you think this should have its own test, we will need another test project in the file system, as none of the file system calls go through an abstraction layer.

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This change is 

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.99%. Comparing base (cd06553) to head (e690bc5).

Files with missing lines	Patch %	Lines
...chine/Corpora/ParatextProjectSettingsParserBase.cs	50.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #402      +/-   ##
==========================================
- Coverage   73.00%   72.99%   -0.01%     
==========================================
  Files         439      439              
  Lines       36672    36672              
  Branches     5036     5037       +1     
==========================================
- Hits        26772    26770       -2     
  Misses       8785     8785              
- Partials     1115     1117       +2     

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