Apply upstream clipper fix 500

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

Applies the fix from AngusJohnson/Clipper2@d18faa9 to our port.

[codecov]

Codecov Report

Merging #272 (52b7d2e) into main (7677cfa) will not change coverage.
The diff coverage is 100%.

@@         Coverage Diff         @@
##           main   #272   +/-   ##
===================================
  Coverage    78%    78%           
===================================
  Files        97     97           
  Lines      5067   5067           
  Branches    932    932           
===================================
  Hits       3985   3985           
  Misses      898    898           
  Partials    184    184           

Flag	Coverage Δ
unittests	78% <100%> (ø)

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Impacted Files	Coverage Δ
...rp.Drawing/Shapes/PolygonClipper/PolygonClipper.cs	64% <100%> (ø)

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