Fix incorrect labels when using encode_sets=TRUE

[krassowski]

Fixes #108.

[codecov-io]

Codecov Report

Merging #110 (113f7a5) into master (e843a8c) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #110      +/-   ##
==========================================
+ Coverage   95.86%   95.92%   +0.06%     
==========================================
  Files           4        4              
  Lines        1498     1498              
==========================================
+ Hits         1436     1437       +1     
+ Misses         62       61       -1     

Impacted Files	Coverage Δ
R/data.R	97.47% <100.00%> (+0.18%)	⬆️

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