fix traceback when disconnecting from BOSH.

src/common/xmpp/dispatcher_nb.py

@@ -462,7 +462,10 @@ class XMPPDispatcher(PlugIn):
 		# we have released dispatcher, so self._owner has no methods
 		if not res:
 			return
-		self._owner.remove_timeout()
+		if 'remove_timeout' in self._owner.__dict__:
+			# When we receive data after we started disconnecting, Transport may
+			# already be plugged out
+			self._owner.remove_timeout()
 		for (_id, _iq) in self._expected.items():
 			if _iq is None:
 				# If the expected Stanza would have arrived, ProcessNonBlocking