by sdl_ufunc_mtx.  Fix up the sdl_ufunc_mtx usage to help prevent errors.

Also, work around a deadlock on Win32 where a video resize event while a
redraw event is later in the queue would deadlock on the vstatlock mutex.

This problem is *not* completely resolved yet.  I think the new scaling
will need to be cached, then applied the next time the queue is empty.