Detect stray clicks in pgdsgui

[timholy]

Fixes #269

[codecov]

Codecov Report

Merging #273 (64a3684) into master (3d34477) will decrease coverage by 0.04%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #273      +/-   ##
==========================================
- Coverage   82.47%   82.43%   -0.05%     
==========================================
  Files          16       16              
  Lines        1900     1901       +1     
==========================================
  Hits         1567     1567              
- Misses        333      334       +1     

Impacted Files	Coverage Δ
src/visualizations.jl	0.00% <0.00%> (ø)

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[timholy]

Test failure on nightly is #274