Oops when clicking the list not under a cell

mitterlib/ui/ui_pygtk.py

@@ -780,6 +780,8 @@ class Interface(object):
         cannot do."""
 
         (model, iter) = view.get_selection().get_selected()
+	if not iter:
+		return
         data = model.get_value(iter, 0)
 
         self._delete_action.set_property('sensitive',