Hiding a view seems to semi-detach any attached OpenGL contexts such that
rendering no longer works.  There's no GL surface for the view.  Calling
-[NSOpenGLContext update] is not sufficient to reattach the context.  So,
fully detach the contexts and reattach them.
Signed-off-by: Ken Thomases <ken@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>