winemac: Sync the frame of the Cocoa view for a window's client area while handling a frame-changed event.

Fixes a problem where the client area view would not be resized as the user
resizes the Cocoa window.
Signed-off-by: Ken Thomases <ken@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>