Fix a panic on close bug

client/client.go

@@ -199,9 +199,11 @@ func NewSubscriber(client *Client, topic string, index int, handler msgbus.Handl
 
 func (s *Subscriber) closeAndReconnect() {
 	s.RLock()
-	s.conn.Close(websocket.StatusNormalClosure, "Closing and reconnecting...")
+	if s.conn != nil {
+		s.conn.Close(websocket.StatusNormalClosure, "Closing and reconnecting...")
+		go s.connect()
+	}
 	s.RUnlock()
-	go s.connect()
 }
 
 func (s *Subscriber) connect() {