1144 handle case when group size is equal to 0 for the LCT model

[lenaploetzke]

Changes and Information

Please briefly list the changes (main added features, changed items, or corrected bugs) made:

• Catch case where the subpopulation size is zero.
• This can happen e.g. if all individuals in the subpopulation die. If this is not handled, we get NaNs in the simulation.

If need be, add additional information and what the reviewer should look out for in particular:

Merge Request - Guideline Checklist

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Checks by code author

• Every addressed issue is linked (use the "Closes #ISSUE" keyword below)
• New code adheres to coding guidelines
• No large data files have been added (files should in sum not exceed 100 KB, avoid PDFs, Word docs, etc.)
• Tests are added for new functionality and a local test run was successful (with and without OpenMP)
• Appropriate documentation for new functionality has been added (Doxygen in the code and Markdown files if necessary)
• Proper attention to licenses, especially no new third-party software with conflicting license has been added
• (For ABM development) Checked benchmark results and ran and posted a local test above from before and after development to ensure performance is monitored.

Checks by code reviewer(s)

• Corresponding issue(s) is/are linked and addressed
• Code is clean of development artifacts (no deactivated or commented code lines, no debugging printouts, etc.)
• Appropriate unit tests have been added, CI passes, code coverage and performance is acceptable (did not decrease)
• No large data files added in the whole history of commits(files should in sum not exceed 100 KB, avoid PDFs, Word docs, etc.)
• On merge, add 2-5 lines with the changes (main added features, changed items, or corrected bugs) to the merge-commit-message. This can be taken from the briefly-list-the-changes above (best case) or the separate commit messages (worst case).

Closes #1144.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.96%. Comparing base (f76d14f) to head (d2b3ff0).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1156      +/-   ##
==========================================
- Coverage   96.98%   96.96%   -0.02%     
==========================================
  Files         142      142              
  Lines       11873    11874       +1     
==========================================
- Hits        11515    11514       -1     
- Misses        358      360       +2     

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[lenaploetzke]

I don't know what happened to the project coverage. Codecov marked an abm file, but that was not changed here.

[reneSchm]

The change looks good. I don't know what is up with the coverage, but this change does not impact tests (especially ones for the ABM).