fix reading in udp conn

app/proxyman/inbound/worker.go

@@ -128,20 +128,23 @@ func (c *udpConn) updateActivity() {
 func (c *udpConn) ReadMultiBuffer() (buf.MultiBuffer, error) {
 	var payload buf.MultiBuffer
 
+	select {
+	case in := <-c.input:
+		payload.Append(in)
+	default:
 		select {
 		case in := <-c.input:
 			payload.Append(in)
 		case <-c.done.Wait():
 			return nil, io.EOF
 		}
+	}
 
 L:
 	for {
 		select {
 		case in := <-c.input:
 			payload.Append(in)
-		case <-c.done.Wait():
-			break L
 		default:
 			break L
 		}