notebook: Make reordering safe for tab disappearance

If the dragged tab is removed during reordering, we need to
call gtk_notebook_stop_reorder(), to clean up and bring the
remaining tabs back in order.

gtk/gtknotebook.c

@@ -5047,6 +5047,8 @@ gtk_notebook_real_remove (GtkNotebook *notebook,
       priv->cur_page = NULL;
       if (next_list && !destroying)
         gtk_notebook_switch_page (notebook, GTK_NOTEBOOK_PAGE (next_list));
+      if (priv->operation == DRAG_OPERATION_REORDER)
+        gtk_notebook_stop_reorder (notebook);
     }
 
   if (priv->detached_tab == list->data)