Catch exception NoneType error in refresh_person

src/cutecoin/gui/community_tab.py

@@ -198,5 +198,8 @@ The process to join back the community later will have to be done again."""
                                      QMessageBox.Ok)
 
     def refresh_person(self, pubkey):
-        index = self.table_community_members.model().sourceModel().person_index(pubkey)
-        self.table_community_members.model().sourceModel().dataChanged.emit(index[0], index[1])
+        if self is None:
+            logging.error("community_tab self is None in refresh_person. Watcher connected to a destroyed tab")
+        else:
+            index = self.table_community_members.model().sourceModel().person_index(pubkey)
+            self.table_community_members.model().sourceModel().dataChanged.emit(index[0], index[1])