check_if_signed: ensure that git-rev-list command succeeds
This makes sure that check_if_signed script will fail if the git-rev-list command fails.
Checklist
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Commits have Signed-off-by:
with name/author being identical to the commit author -
Code modified for feature
Reviewer's checklist:
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Any issues marked for closing are addressed -
There is a test suite reasonably covering new functionality or modifications -
Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
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This feature/change has adequate documentation added -
No obvious mistakes in the code