Guard against undefined in CoreGetFeatureDetails

[cmdcolin]

Fixes #3674

[cmdcolin]

could consider the entire 'soundness' of this operation perhaps as a separate issue, but this should avoid some crashes (that were observed under load by @carolinebridge-oicr )

[codecov]

Codecov Report

Merging #3681 (23c4584) into main (ba81be7) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3681      +/-   ##
==========================================
+ Coverage   62.62%   62.64%   +0.01%     
==========================================
  Files         892      892              
  Lines       30252    30249       -3     
  Branches     7321     7321              
==========================================
+ Hits        18946    18948       +2     
+ Misses      11123    11118       -5     
  Partials      183      183              

Impacted Files	Coverage Δ
...lugins/alignments/src/LinearPileupDisplay/model.ts	66.25% <ø> (ø)
packages/core/rpc/methods/CoreGetFeatureDetails.ts	77.77% <100.00%> (-3.18%)	⬇️

... and 3 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more