cocoa: Force an OpenGL context update when the window becomes key.

Fixes missing rendering on macOS 10.14 ("Mojave").

Fixes Bugzilla #4272.
(transplanted from 55489adbb75c8eb7c7719a3f9c85a15d06df2f27)

--HG--
branch : SDL-ryan-batching-renderer
extra : transplant_source : UH%9A%DB%B7%5C%8E%B7%C7q%9A%3F%9C%85%A1%5D%06%DF/%27
1 file changed