Correct a small oversight

When changing themes, we also need to update the box spacing of
tooltips.

gtk/gtktooltip.c

@@ -475,6 +475,8 @@ gtk_tooltip_window_style_set (GtkTooltip *tooltip)
 			     tooltip->window->style->ythickness,
 			     tooltip->window->style->xthickness,
 			     tooltip->window->style->xthickness);
+  gtk_box_set_spacing (GTK_BOX (tooltip->hbox,
+		       tooltip->window->style->xthickness);
 
   gtk_widget_queue_draw (tooltip->window);
 }