Fix infinite loop on single match

[abhinav]

If there's a single entry in the collection of matches, our huffman
implementation will return an empty label. That results in an infinite
loop when rendering because we attempt to match empy input to an empty
label.

Resolve this by handling the single match case separately.

Fixes #38

[codecov-commenter]

Codecov Report

Merging #39 (88db35f) into main (3561e26) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
+ Coverage   73.70%   73.77%   +0.06%     
==========================================
  Files          29       29              
  Lines        1563     1567       +4     
==========================================
+ Hits         1152     1156       +4     
  Misses        390      390              
  Partials       21       21              

Impacted Files	Coverage Δ
internal/huffman/huffman.go	97.01% <100.00%> (+0.18%)	⬆️

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