Optional includeLength in encryption
Optional includeLength in encryption

Hi,
I was interchanging messages with a 3rd Party service and the encryptions were different, so we dig in the code, in both implementations and found that the `includeLenght` in `_toUint8List` `_toUint32List` was the variable that was making all different, so I just added as optional
xxtea/xxtea-dart