waived an unnecessary IllegalArgumentException in PairHMM

[davidbenjamin]

Closes #5543.

@kachulis Could you review this PR?

[codecov-io]

Codecov Report

Merging #5705 into master will increase coverage by 0.002%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #5705       +/-   ##
===============================================
+ Coverage     87.066%   87.068%   +0.002%     
- Complexity     31853     31854        +1     
===============================================
  Files           1940      1940               
  Lines         146679    146678        -1     
  Branches       16218     16218               
===============================================
+ Hits          127707    127709        +2     
+ Misses         13060     13059        -1     
+ Partials        5912      5910        -2

Impacted Files	Coverage Δ	Complexity Δ
...oadinstitute/hellbender/utils/pairhmm/PairHMM.java	78.417% <ø> (+0.56%)	24 <0> (ø)	⬇️
...nder/utils/runtime/StreamingProcessController.java	68.246% <0%> (+0.948%)	34% <0%> (+1%)	⬆️

[lbergelson]

Ah, @TedBrookings it looks like your initial thought was right and I was too cautious :)

[kachulis]

Looks good to me!