deal with deleting handlers that are no longer there

sleekxmpp/xmlstream/xmlstream.py

@@ -490,7 +490,10 @@ class XMLStream(object):
                 # processed in the queue.
                 with self.__event_handlers_lock:
                     handler_index = self.__event_handlers[name].index(handler)
+                    try:
                         self.__event_handlers[name].pop(handler_index)
+                    except:
+                        pass
 
     def schedule(self, name, seconds, callback, args=None,
                  kwargs=None, repeat=False):