Prevent potential issues with undoing/redoing changes to loop conditions

[soininen]

A small fix potentially preventing a bug.

Re #2925

Checklist before merging

• Documentation is up-to-date
• Release notes have been updated
• Unit tests have been added/updated accordingly
• Code has been formatted by black & isort
• Unit tests pass

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 66.86%. Comparing base (47a949f) to head (56e774d).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
spinetoolbox/project_commands.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2926      +/-   ##
==========================================
+ Coverage   66.85%   66.86%   +0.01%     
==========================================
  Files         190      190              
  Lines       37027    37027              
  Branches     6355     6355              
==========================================
+ Hits        24755    24759       +4     
+ Misses      10951    10945       -6     
- Partials     1321     1323       +2     

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