Reverse hierarchy of wxPizza GdkWindows

widget->window must be topmost in order for GTK+ to calculate DND drop coordinates correctly
fixes #11834


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63775 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/glcanvas.cpp

@@ -247,7 +247,7 @@ bool wxGLCanvas::Create(wxWindow *parent,
 
 Window wxGLCanvas::GetXWindow() const
 {
-    GdkWindow *window = m_wxwindow->window;
+    GdkWindow* window = GTKGetDrawingWindow();
     return window ? GDK_WINDOW_XWINDOW(window) : 0;
 }