Do not return zero-length alignments

[nh13]

This occurs when performing local alignment and setting the minimum
score to zero or smaller.

[codecov-io]

Codecov Report

Merging #552 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #552      +/-   ##
==========================================
+ Coverage   94.96%   95.03%   +0.06%     
==========================================
  Files         104      104              
  Lines        5863     5863              
  Branches      399      371      -28     
==========================================
+ Hits         5568     5572       +4     
+ Misses        295      291       -4

Impacted Files	Coverage Δ
.../scala/com/fulcrumgenomics/alignment/Aligner.scala	96.89% <100%> (+2.48%)	⬆️

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[tfenne]

Does this effect the methods that return the single best alignment? Maybe just add a line in the test to call align(query, target) and ensure it still returns a result?

[nh13]

@tfenne I updated the commit for local alignment in Aligner.findBest. This must return an alignment, but since local alignment has a minimum score of zero by definition, it will return an "empty" alignment (i.e. the cigar is empty). It probably would be better to return an Option[Alignment], but this is fine for now.