Fixed +/- crash

[flabbet]

Fixes #216

[codecov-commenter]

Codecov Report

Merging #217 (fce881d) into master (a3eee57) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #217      +/-   ##
==========================================
- Coverage   45.16%   45.15%   -0.02%     
==========================================
  Files         303      303              
  Lines       12116    12119       +3     
  Branches     1223     1224       +1     
==========================================
  Hits         5472     5472              
- Misses       6373     6376       +3     
  Partials      271      271              

Impacted Files	Coverage Δ
...ViewModels/SubViewModels/Main/ViewportViewModel.cs	34.78% <0.00%> (-5.22%)	⬇️

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