[GTKUI] Only save_state when mainwindow is visible

* A similar fix (550ddc01) was applied to develop so backporting to guard
   against similar problems with columns not saving properly.

deluge/ui/gtkui/torrentview.py

@@ -350,13 +350,13 @@ class TorrentView(listview.ListView, component.Component):
 
     def shutdown(self):
         """Called when GtkUi is exiting"""
-        if self.window.visible():
         self.save_state()
 
     def save_state(self):
         """
         Saves the state of the torrent view.
         """
+        if self.window.visible():
             listview.ListView.save_state(self, "torrentview.state")
 
     def remove_column(self, header):