Fix handling of results with unknown timestamps

[daniel-thom]

No description provided.

[github-actions]

Performance Results

Version	Precompile Time
Main	8.666655971
This Branch	8.703524457

Version	Build Time
Main-Build Time Precompile	77.01813601
Main-Build Time Postcompile	4.794826714
This Branch-Build Time Precompile	78.442498249
This Branch-Build Time Postcompile	4.880074556

[codecov]

Codecov Report

Merging #1008 (ec73184) into main (e69e29d) will decrease coverage by 0.03%.
The diff coverage is 76.92%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1008      +/-   ##
==========================================
- Coverage   80.26%   80.23%   -0.03%     
==========================================
  Files         116      116              
  Lines       12313    12276      -37     
==========================================
- Hits         9883     9850      -33     
+ Misses       2430     2426       -4     

Flag	Coverage Δ
unittests	80.23% <76.92%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
...rc/simulation/decision_model_simulation_results.jl	97.00% <66.66%> (-1.77%)	⬇️
src/core/results_by_time.jl	47.72% <100.00%> (+2.48%)	⬆️

... and 15 files with indirect coverage changes