[Equil] Handle factorization errors in initial estimator

[speth]

Changes proposed in this pull request

• Catch and ignore factorization errors in ChemEquil::estimateElementPotentials

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Closes #1473

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Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

Merging #1479 (6d808f6) into main (055a530) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main    #1479      +/-   ##
==========================================
- Coverage   70.05%   70.05%   -0.01%     
==========================================
  Files         377      377              
  Lines       57788    57789       +1     
  Branches    19410    19410              
==========================================
  Hits        40482    40482              
- Misses      14745    14747       +2     
+ Partials     2561     2560       -1     

Impacted Files	Coverage Δ
src/equil/ChemEquil.cpp	68.82% <50.00%> (-0.09%)	⬇️

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[ischoegl]

Thanks, @speth - looks good to me!