Fix double accounting of border width

For csd, we were subtracting the border width one too many
times from the child height, causing clipped off content e.g.
in the 'Properties' window in testgtk.

gtk/gtkwindow.c

@@ -6073,7 +6073,9 @@ _gtk_window_set_allocation (GtkWindow           *window,
                             title_border.top +
                             title_border.bottom;
       child_allocation.width -= window_border.left + window_border.right;
-      child_allocation.height -= child_allocation.y + window_border.bottom;
+      child_allocation.height -= window_border.top + window_border.bottom +
+                                title_border.top + title_border.bottom +
+                                title_height;
     }
 
   if (gtk_widget_get_realized (widget))