winex11.drv: Make sure that default clipping region exists before calling ExcludeUpdateRgn().

[Alexandre Julliard]

Dmitry Timoshkov <dmitry at codeweavers.com> writes:

> If there is no current clipping region ExtSelectClipRgn(hdc, hrgn, RGN_DIFF)
> creates its own default clipping region which in most cases doesn't match
> neither a visible region nor the window extents attached to the DC.

It will get intersected with the visible region anyway, so it shouldn't
matter as long as it's large enough. Why does it make a difference?

-- 
Alexandre Julliard
julliard at winehq.org