applied the workaround for XUnionRectWithRegion() returning ampty result if the rect is empty to wxX11 and wxMotif as well

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@17046 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/x11/region.cpp

@@ -149,6 +149,12 @@ void wxRegion::Clear()
 
 bool wxRegion::Union( wxCoord x, wxCoord y, wxCoord width, wxCoord height )
 {
+    // work around for XUnionRectWithRegion() bug: taking a union with an empty
+    // rect results in an empty region (at least XFree 3.3.6 and 4.0 have this
+    // problem)
+    if ( !width || !height )
+        return TRUE;
+
     XRectangle rect;
     rect.x = x;
     rect.y = y;