SetupWindowData in SDL_X11window.c was realloc()ing the display window list and incrementing numwindows even though those are being updated in functions that call
this function. The result is that it is possible to get the same window added to the list twice.

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extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%402738