Complete polygon mask when saving parameters

[dagewa]

If the user is creating a polygon mask they previously had to click on a different mode (e.g. Circle) to complete the mask description, before clicking on Save mask.phil, otherwise an empty mask description was written out.

This change resolves that, by forcing the polygon values to be added when OnUpdate is called, and then calling OnUpdate when the Save button is clicked.

[codecov]

Codecov Report

Merging #2150 (09c8f6e) into main (178236f) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2150   +/-   ##
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  Coverage   80.63%   80.64%           
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  Files         587      587           
  Lines       66417    66417           
  Branches     9357     9357           
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+ Hits        53557    53562    +5     
+ Misses      10804    10802    -2     
+ Partials     2056     2053    -3