Sometimes the clipping region can become bigger than the

Sometimes the clipping region can become bigger than the
actual window, and this can cause X11 to fail inside gdk_gc_set_clip_region
intermittently. The clipping region is now limited to the actual
window size so only valid regions can be passed to this function.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@25254 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775