Disco: maximum recursion depth exceeded

[steve-e]

Happened when I played around with Service Discovery on jabber.ru

Traceback (most recent call last):
  File "projekte/python/gajim/src/common/xmpp/idlequeue.py", line 132, in process_events
    obj.pollin()
  File "projekte/python/gajim/src/common/xmpp/transports_nb.py", line 361, in pollin
    self._do_receive()
  File "projekte/python/gajim/src/common/xmpp/transports_nb.py", line 500, in _do_receive
    self.on_receive(received)
  File "projekte/python/gajim/src/common/xmpp/dispatcher_nb.py", line 352, in dispatch
    handler['func'](session,stanza)
  File "projekte/python/gajim/src/common/connection_handlers.py", line 700, in _DiscoverItemsCB
    self.dispatch('AGENT_INFO_ITEMS', (jid, node, items))
  File "projekte/python/gajim/src/common/connection.py", line 158, in dispatch
    self.put_event((event, data))
  File "projekte/python/gajim/src/common/connection.py", line 154, in put_event
    gajim.handlers[ev[0]](self.name, ev[1])
  File "gajim.py", line 954, in handle_event_agent_info_items
    array[1], array[2])
  File "projekte/python/gajim/src/disco.py", line 369, in agent_items
    cb(jid, node, items)
  File "projekte/python/gajim/src/disco.py", line 214, in __call__
    return cb(*args, **kwargs)
  File "projekte/python/gajim/src/disco.py", line 1838, in _add_items
    self._add_item(jid, node, item, force)
  File "projekte/python/gajim/src/disco.py", line 1863, in  add_item
 [.... repeated x tousend times]
  File "projekte/python/gajim/src/disco.py", line 1863, in _add_item
    args = (force,))
  File "projekte/python/gajim/src/disco.py", line 325, in get_items
    args = (self._items[addr],) + args
  File "projekte/python/gajim/src/disco.py", line 156, in __getitem__
    return item()
RuntimeError: maximum recursion depth exceeded

[asterix]

(In [8381]) prevent loop is pubsub disco (even if server answer looks strange) fixes #3292