fixes #4657 - traceback on terminating stanza after BOSH init request

src/common/xmpp/client_nb.py

@@ -310,6 +310,14 @@ class NonBlockingClient:
 				self._xmpp_connect_machine(
 					mode='FAILURE',
 					data='Error on stream open')
+				return
+
+			# if terminating stanza was received after init request then client gets
+			# disconnected from bosh transport plugin and we have to end the stream
+			# negotiating process straight away.
+			# fixes #4657
+			if not self.connected: return
+
 			if self.incoming_stream_version() == '1.0':
 				if not self.got_features:
 					on_next_receive('RECEIVE_STREAM_FEATURES')