Fix buildrelease for when there are no changes between releases

[amaltaro]

Fixes #11640

Status

ready

Description

Fixes an issue introduced with #11645
Whenever we cut a new release on top of another one, without any commits in between, the script was crashing with:

$ ./bin/buildrelease.sh -t 2.2.2rc7
Checking out branch: master
Already on 'master'
Building new release of WMCore 2.2.2rc7 on master
Updating version string ...
Generating CHANGES file
sed: -e expression #1, char 0: no previous regular expression

So here we check whether there is an actual commit line to be checked.

Is it backward compatible (if not, which system it affects?)

YES

Related PRs

Fix bug introduced with #11645

External dependencies / deployment changes

None

[amaltaro]

This has been tested in both scenarios:

1. with changes to be considered
2. without any changes

[cmsdmwmbot]

Jenkins results:

• Python3 Unit tests: succeeded
• Python3 Pylint check: succeeded
• Pylint py3k check: succeeded
• Pycodestyle check: succeeded

Details at https://cmssdt.cern.ch/dmwm-jenkins/view/All/job/DMWM-WMCore-PR-test/14314/artifact/artifacts/PullRequestReport.html

[todor-ivanov]

looking good