Properly lock before the close check

pubsub.go

@@ -118,6 +118,8 @@ func (t *TwitchPubSub) Close() error {
 		t.listening = nil
 	}
 
+	t.Lock()
+
 	if t.wsConn != nil {
 		// To cleanly close a connection, a client should send a close
 		// frame and wait for the server to close the connection.