Disconnect Graph view signals in closeEvent()

The signals should be disconnected once when we close the view.
tear_down() gets called also when we add new databases to the editor
tab.

Author: soininen

spinetoolbox/spine_db_editor/widgets/graph_view_mixin.py

@@ -1013,13 +1013,6 @@ def get_open_file_path(self, group, caption, filters):
         self.qsettings.endGroup()
         return file_path
 
-    def tear_down(self):
-        if not super().tear_down():
-            return False
-        self.db_mngr.items_added.disconnect(self._refresh_icons)
-        self.db_mngr.items_updated.disconnect(self._refresh_icons)
-        return True
-
     def closeEvent(self, event):
         """Handle close window.
 
@@ -1029,6 +1022,8 @@ def closeEvent(self, event):
         super().closeEvent(event)
         if not event.isAccepted():
             return
+        self.db_mngr.items_added.disconnect(self._refresh_icons)
+        self.db_mngr.items_updated.disconnect(self._refresh_icons)
         if self.scene is not None:
             self.scene.deleteLater()
         # Make sure the fetch parent isn't used to remove discarded changes after we've deleted the graph scene.