plugin XEP-0045: display a note when no configuration is available on the room

sat/plugins/plugin_xep_0045.py

@@ -280,6 +280,9 @@ class XEP_0045(object):
             return defer.fail(exceptions.DataError)
 
         def xmluiReceived(xmlui):
+            if not xmlui:
+                msg = D_(u"No configuration available for this room")
+                return {"xmlui": xml_tools.note(msg).toXml()}
             return {"xmlui": xmlui.toXml()}
         return self.configureRoom(client, room_jid).addCallback(xmluiReceived)