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

[Dmitry Timoshkov]

Alexandre Julliard <julliard at winehq.org> wrote:

> > 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?

I looks like the default clip region created by ExtSelectClipRgn() uses
the dimensions of the selected bitmap, and it's not large enough.

-- 
Dmitry.