stream/mts: fixed what encoder is doing with Write methods int return

stream/mts/encoder.go

@@ -220,9 +220,9 @@ func (e *Encoder) Write(nalu []byte) (int, error) {
 			pkt.PCR = e.pcr()
 			pusi = false
 		}
-		n, err := e.dst.Write(pkt.Bytes(e.tsSpace[:PacketSize]))
+		_, err := e.dst.Write(pkt.Bytes(e.tsSpace[:PacketSize]))
 		if err != nil {
-			return n, err
+			return len(nalu), err
 		}
 		e.pktCount++
 	}