Sast checks #129

SonarQube reveal two issues (could be refactored):

1. Delete this unreachable code or refactor the code to make it reachable (in both variants of validation crc/sha we have return statements):
   

   gitdb/gitdb/pack.py

   Line 851 in f8fdfec

   return True

2. This branch duplicates the one on line 268.
   

   gitdb/gitdb/pack.py

   Line 270 in f8fdfec

   elif attr == "_packfile_checksum":

   
   and
   

   gitdb/gitdb/pack.py

   Line 268 in f8fdfec

   if attr == "_packfile_checksum":