Decoding fails if the data's first byte is 0

[nazariyg]

Example:

let bytes: [UInt8] = [0, 128, 128, 128]
let encodedString = Base58.base58CheckEncode(bytes)
let decodedBytes = Base58.base58CheckDecode(encodedString)!  // <- fails here

[asloup]

Yeah, I think the bug is in base58Decode because it's handling things as a big int, which considers leading 0s as insignificant - for example, 000123456 is the same as 123456. But for our case, those leading 0s represent 0x00 bytes, thus they are significant. So we just need to prefix them back to the decoded bytes before returning.

Bug
return Array(byteString.prefix { i in i == alphabet[0] }) + bytes

Fix

let zeroBytesToAdd = byteString.prefix { i in i == alphabet[0] }.count
return [UInt8](repeating: 0, count: zeroBytesToAdd) + bytes

[asloup]

Just checked the PRs too. Looks like this one would fix it: #21