Check whether path is a valid git folder

[bearzk]

before running all calculation against it.

It runs 2 git commands to see if the folder
is a git folder and if it contains commits.

[codecov]

Codecov Report

Merging #181 into master will decrease coverage by 2.75%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master     #181      +/-   ##
============================================
- Coverage     76.32%   73.57%   -2.76%     
- Complexity      109      113       +4     
============================================
  Files            17       17              
  Lines           321      333      +12     
============================================
  Hits            245      245              
- Misses           76       88      +12

Impacted Files	Coverage Δ	Complexity Δ
src/Results/ResultCollection.php	100% <ø> (ø)	6 <0> (ø)	⬇️
src/Managers/ProcessManager.php	0% <ø> (ø)	8 <0> (ø)	⬇️
src/Logic/ResultsLogic.php	100% <ø> (ø)	2 <0> (ø)	⬇️
src/Results/Result.php	96% <ø> (ø)	6 <0> (ø)	⬇️
src/Collections/FileCollection.php	100% <ø> (ø)	2 <0> (ø)	⬇️
src/Results/ResultsParser.php	100% <ø> (ø)	5 <0> (ø)	⬇️
src/Commands/ChurnCommand.php	0% <0%> (ø)	10 <3> (+4)	⬆️

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[villfa]

Thank you for the work.

I'm closing it since #257 and #260 fix the same problem.