fast return on zero ack list

transport/internet/kcp/sending.go

@@ -255,6 +255,10 @@ func (v *SendingWorker) ProcessSegment(current uint32, seg *AckSegment, rto uint
 	}
 	v.ProcessReceivingNextWithoutLock(seg.ReceivingNext)
 
+	if seg.Count == 0 {
+		return
+	}
+
 	var maxack uint32
 	var maxackRemoved bool
 	for i := 0; i < int(seg.Count); i++ {