Invalid characters for a wallet name, e.g. `bitcoin-qt -wallet=你好` used to result in an error like this

<img width="494" alt="schermafbeelding 2018-07-24 om 17 46 37" src="https://user-images.githubusercontent.com/10217/43150553-7bdf598a-8f6a-11e8-8972-44c311a57e56.png">

But now it just crashes:

<img width="509" alt="schermafbeelding 2018-07-24 om 17 43 26" src="https://user-images.githubusercontent.com/10217/43150605-9cf32192-8f6a-11e8-9333-87d074c8dd35.png">

I didn't do a `git bisect`, but it broke somewhere this year :-)
LOCK2(cs_main, cs_wallet);
    CReserveKey reservekey(this);
    CTransactionRef tx_new;
    if (!CreateTransaction(vecSend, tx_new, reservekey, nFeeRet, nChangePosInOut, strFailReason, coinControl, false)) {
        return false;
    }
    if (nChangePosInOut != -1) {
        tx.vout.insert(tx.vout.begin() + nChangePosInOut, tx_new->vout[nChangePosInOut]);
        
        
        reservekey.KeepKey();
    }
    
    
    for (unsigned int idx = 0; idx < tx.vout.size(); idx++) {
        tx.vout[idx].nValue = tx_new->vout[idx].nValue;
    }
    
    for (const CTxIn& txin : tx_new->vin) {
        if (!coinControl.IsSelected(txin.prevout)) {
            tx.vin.push_back(txin);
            if (lockUnspents) {
                LockCoin(txin.prevout);
            }
        }
    }
    return true;
}
OutputType CWallet::TransactionChangeType(OutputType change_type, const std::vector<CRecipient>& vecSend)