Don't fail all-reports.py when branch history is missing

[AnHeuermann]

Issue

Fixes #277.

Changes

• If the history HTML for a branch is missing the script fails. E.g. if v1.26-cpp is missing all other branches afterwards aren't reported any more.

[AnHeuermann]

@adrpo should we run a Cpp job in addition so we create the history HTML for it or remove branch v1.26-cpp from the command line arguments provided by Jenkins?

[AnHeuermann]

Let's see if https://test.openmodelica.org/jenkins/job/LibraryTesting/job/LibraryTest/10755/ succeeds the reports stage.

[adrpo]

@adrpo should we run a Cpp job in addition so we create the history HTML for it or remove branch v1.26-cpp from the command line arguments provided by Jenkins?

I thought I added history/v1.26-cpp/00_history.txt, yes, it seems so: https://libraries.openmodelica.org/branches/history/v1.26-cpp/

I think we should create these things automatically via ssh commands.