Fix bugs before release

[MaGering]

Fix #264
With this PR bugs are fixed before the release of pvcompare.

The following steps were realized, as well (if applies):

• Use in-line comments to explain your code
• Write docstrings to your code
• For new functionalities: Explain in readthedocs
• Write test(s) for your new patch of code
• Update the CHANGELOG.md (let's start this after the first release)
• Apply black (black . --exclude docs/)
• Check if full simulation tests pass locally (EXECUTE_TESTS_ON=master pytest)
  ---> passes at first run
  ===== 75 passed, 67 warnings in 125.44s (0:02:05) ======

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_{For more information on how to contribute check the CONTRIBUTING.md.}

[SabineHaas]

@MaGering I think #264 should be fixed before the release

[MaGering]

@MaGering I think #264 should be fixed before the release

I fixed it with commit 15da7db.