(#140) Return error if one of the commands on pipes fails

[sergiomb2]

Description

I consider it a bugfix , but please review it before merge , the goal is be merged before the next release

Type of Change

• Bug fix (targets 0.4.x)
• New feature (targets master)
• Documentation update
• Other (please describe)

Testing

check if all gitdiff, gitdiffview, gitshow, gitshowview, svndiff, svndiffview are working as expect.
run gitdiff, gitdiffview, gitshow, gitshowview, svndiff, svndiffview outside of one git repo tree and check if return error without pipe to the next comand

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.60%. Comparing base (284019c) to head (d38a1f6).
⚠️ Report is 1 commits behind head on 0.4.x.

Additional details and impacted files

@@           Coverage Diff           @@
##            0.4.x     #149   +/-   ##
=======================================
  Coverage   83.60%   83.60%           
=======================================
  Files           5        5           
  Lines        4190     4190           
  Branches      995      995           
=======================================
  Hits         3503     3503           
  Misses        687      687           

Flag	Coverage Δ
unittests	83.60% <ø> (ø)

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