Issue where BigInt.toByteArrayUnsigned returns 31 bytes

[Ninkip2p]

Here is an example root key:
tprv8ZgxMBicQKsPetSeaqxJJLxz6rRvxz2fuTBKt4ntiqRjTAdmqkqdFKDCX9X9dgPLcEXELNSADqXkDzHs77WJcP6wDvQ5XcX7k5UxBiAZTzH

For some reason BigInt.toByteArrayUnsigned returns byte array without the leading 0 byte, inserting this into the byte array in the case of the length being 31 seems to fix this

[anaoum]

I just submitted a pull request #5 for this bug. Hopefully it gets merged soon as this can go dangerously unnoticed by the end user.

[bip32JP]

Found another place where toByteArrayUnsigned() did some funky stuff...