Settings: Fix pylint errors

gajim/gtk/settings.py

@@ -635,6 +635,7 @@ def get_setting_value(self):
 class ChangePasswordSetting(DialogSetting):
     def __init__(self, *args, **kwargs):
         DialogSetting.__init__(self, *args, **kwargs)
+        self.change_dialog = None
 
     def show_dialog(self, parent):
         try: