In my System.Drawing test run, I got some failures in MonoTests.System.Drawing.GDIPlusTest:DisposeImage_Dual. I don't think this is an indication that the patch is wrong, in fact a similar test is commented out in Wine because it can crash: https://gitlab.winehq.org/wine/wine/-/blob/master/dlls/gdiplus/tests/image.c...
I also found that DisposeImage_Dual works when run on it's own, I only get the failures when running it with the other tests in the GDIPlusTest class.
It suggests that this change might make this particular crash in GdipDisposeImage more likely, so I wanted to make a note of it here.