fix: conn nil

pkg/mqtt/connection.go

@@ -321,11 +321,9 @@ func (c *Connection) SendMsgToClient() {
 		case <-c.closeChan:
 			return
 		case msg, ok := <-c.SendChan:
-			c.mLock.Lock()
 			if c.Conn == nil {
 				return
 			}
-			c.mLock.Unlock()
 			if !ok {
 				server.Log.Errorf("%s is end now", host)
 				return