Omit unparseable dates

[jwodder]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.03%. Comparing base (6db870c) to head (999605f).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/mailbits/email2dict.py	60.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #16      +/-   ##
==========================================
- Coverage   96.88%   96.03%   -0.86%     
==========================================
  Files           3        3              
  Lines         225      227       +2     
  Branches       34       36       +2     
==========================================
  Hits          218      218              
  Misses          3        3              
- Partials        4        6       +2     

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