Reported by @kallewoof here: https://github.com/bitcoin/bitcoin/pull/13917#issuecomment-412459298

```
$ ./bitcoin-cli createpsbt "[]" "[{\"$(./bitcoin-cli getnewaddress)\":0.01}]"
cHNidP8BACoCAAAAAAFAQg8AAAAAABepFG6Rty1Vk+fUOR4v9E6R6YXDFkHwhwAAAAAAAA==
$ ./bitcoin-cli decodepsbt cHNidP8BACoCAAAAAAFAQg8AAAAAABepFG6Rty1Vk+fUOR4v9E6R6YXDFkHwhwAAAAAAAA==
error code: -22
error message:
TX decode failed CDataStream::read(): end of data: unspecified iostream_category error
```

throw std::ios_base::failure("Final scriptSig key is more than one byte type");
                    }
                    s >> final_script_sig;
                    break;
                }
                case PSBT_IN_SCRIPTWITNESS:
                {
                    if (!final_script_witness.IsNull()) {
                        throw std::ios_base::failure("Duplicate Key, input final scriptWitness already provided");
                    } else if (key.size() != 1) {
                        throw std::ios_base::failure("Final scriptWitness key is more than one byte type");
                    }
                    UnserializeFromVector(s, final_script_witness.stack);
                    break;
                }
                
                default:
                    if (unknown.count(key) > 0) {
                        throw std::ios_base::failure("Duplicate Key, key for unknown value already provided");
                    }
                    
                    std::vector<unsigned char> val_bytes;
                    s >> val_bytes;
                    unknown.emplace(std::move(key), std::move(val_bytes));
                    break;
            }
        }
    }
    template <typename Stream>
    PSBTInput(deserialize_type, Stream& s) {