Fix sensitivities w.r.t. unused log-scaled NaN parameters

[dweindl]

When applying the chain rule factor, avoid NaN-propagation in case of zero-multiplications.

(Will allow enabling the ExampleJakstatAdjoint.SensitivityAdjointUnusedNanOutputs test (#686) after #2898.)

[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.66%. Comparing base (f83f92d) to head (02851bc).
⚠️ Report is 59 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rdata.cpp	70.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2903      +/-   ##
==========================================
- Coverage   80.28%   79.66%   -0.62%     
==========================================
  Files         330      330              
  Lines       22660    22669       +9     
  Branches     1531     1538       +7     
==========================================
- Hits        18192    18059     -133     
- Misses       4458     4600     +142     
  Partials       10       10              

Flag	Coverage Δ
cpp	75.44% <70.00%> (-0.04%)	⬇️
cpp_python	33.73% <33.33%> (+<0.01%)	⬆️
petab	39.13% <23.33%> (-0.02%)	⬇️
python	74.40% <60.00%> (-0.05%)	⬇️
sbmlsuite-jax	?

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Files with missing lines	Coverage Δ
src/rdata.cpp	93.03% <70.00%> (-0.36%)	⬇️

... and 8 files with indirect coverage changes

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