Correct out of range checking

Author: tanghaowillow

Diff for: transport_layer_cc.go

@@ -523,17 +523,20 @@ func (t *TransportLayerCC) Unmarshal(rawPacket []byte) error { //nolint:gocognit
 
 	recvDeltasPos := packetStatusPos
 	for _, delta := range t.RecvDeltas {
-		if recvDeltasPos >= totalLength {
-			return errPacketTooShort
-		}
 		if delta.Type == TypeTCCPacketReceivedSmallDelta {
+			if recvDeltasPos+1 > totalLength {
+				return errPacketTooShort
+			}
 			err := delta.Unmarshal(rawPacket[recvDeltasPos : recvDeltasPos+1])
 			if err != nil {
 				return err
 			}
 			recvDeltasPos++
 		}
 		if delta.Type == TypeTCCPacketReceivedLargeDelta {
+			if recvDeltasPos+2 > totalLength {
+				return errPacketTooShort
+			}
 			err := delta.Unmarshal(rawPacket[recvDeltasPos : recvDeltasPos+2])
 			if err != nil {
 				return err