When wrapping a foreign W32 window, don't forget to store its HWND

When that window is later used as a parent for a GDK child, the call to
CreateWindow*() will fail, because its HWND is 0.

https://bugzilla.gnome.org/show_bug.cgi?id=733768

gdk/win32/gdkwindow-win32.c

@@ -742,6 +742,7 @@ gdk_win32_window_foreign_new_for_display (GdkDisplay      *display,
   window->viewable = TRUE;
 
   window->depth = gdk_visual_get_system ()->depth;
+  GDK_WINDOW_HWND (window) = anid;
 
   g_object_ref (window);
   gdk_win32_handle_table_insert (&GDK_WINDOW_HWND (window), window);