fixed incorrect computation of window's visible area: window's position was added once too much

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41517 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/dfb/dcclient.cpp

@@ -45,7 +45,7 @@
 // boundaries ("hidden behind its borders"), recursively:
 static wxRect GetUncoveredWindowArea(wxWindow *win)
 {
-    wxRect r(win->GetRect());
+    wxRect r(win->GetSize());
 
     if ( win->IsTopLevel() )
         return r;