Fix pubsub get_items.

- item_ids checked for None
- pubsub node is set

sleekxmpp/plugins/xep_0060/pubsub.py

@@ -355,8 +355,10 @@ class xep_0060(base_plugin):
         many items, so an iterator can be returned if needed.
         """
         iq = self.xmpp.Iq(sto=jid, sfrom=ifrom, stype='get')
+        iq['pubsub']['items']['node'] = node
         iq['pubsub']['items']['max_items'] = max_items
 
+        if item_ids is not None:
             for item_id in item_ids:
                 item = self.stanza.Item()
                 item['id'] = item_id