coverage_report: Gracefully handle missing file

[Javagedes]

Check if the file exists in the workspace before passing to pygount for source code analysis. If it does not exist, skip the file.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.58%. Comparing base (bf643b0) to head (ef6e79d).
Report is 58 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #814      +/-   ##
==========================================
- Coverage   78.75%   78.58%   -0.17%     
==========================================
  Files          49       49              
  Lines        4909     4936      +27     
==========================================
+ Hits         3866     3879      +13     
- Misses       1043     1057      +14     

see 2 files with indirect coverage changes