Some commands of `bitcoin-tx` accept an index of an existing input/output, e.g. `delin` or `delout`.  And while the index is checked for being out-of-bounds, garbage (non-numeral characters) are happily accepted.  All of the following are fine:

    $ bitcoin-tx -create outaddr=1:1M72Sfpbz1BPpXFHz9m3CdqATR44Jvaydd delout=
    $ bitcoin-tx -create outaddr=1:1M72Sfpbz1BPpXFHz9m3CdqATR44Jvaydd delout=foobar
    $ bitcoin-tx -create outaddr=1:1M72Sfpbz1BPpXFHz9m3CdqATR44Jvaydd delout=0bla

I think all of them should throw an error instead of silently treating the index as zero.

The reason for this is that internally, `atoi` is called - and that by design discards anything after the first non-numeric character (and may just return zero if there are no numerals at all).

A possible fix would be to use `strtol` instead and to verify that the returned `endptr` is actually the end of the input string.  Alternatively, one could convert the integer back to a string and require that it matches the input string exactly.
ECC_Start();
    }
    ~Secp256k1Init() {
        ECC_Stop();
    }
};
static void MutateTx(CMutableTransaction& tx, const std::string& command,
                     const std::string& commandVal)
{
    std::unique_ptr<Secp256k1Init> ecc;
    if (command == "nversion")
        MutateTxVersion(tx, commandVal);
    else if (command == "locktime")
        MutateTxLocktime(tx, commandVal);
    else if (command == "replaceable") {
        MutateTxRBFOptIn(tx, commandVal);
    }
    else if (command == "delin")
        MutateTxDelInput(tx, commandVal);
    else if (command == "in")
        MutateTxAddInput(tx, commandVal);
    else if (command == "delout")
        MutateTxDelOutput(tx, commandVal);
    else if (command == "outaddr")
        MutateTxAddOutAddr(tx, commandVal);
    else if (command == "outpubkey") {
        ecc.reset(new Secp256k1Init());
        MutateTxAddOutPubKey(tx, commandVal);
    } else if (command == "outmultisig") {