winemac: Invalidate cached hasGLDescendant value unconditionally when the view is hidden or unhidden.

Even if the (un)hidden view doesn't have attached GL contexts itself, its
descendants may.  It doesn't make sense not to check them just because this
view doesn't have GL contexts.
Signed-off-by: Ken Thomases <ken@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>