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 :-)
{
    WalletBatch batch(*database);
    if (!batch.TxnBegin())
        return false;
    int64_t nNow = GetAdjustedTime();
    
    CAccountingEntry debit;
    debit.nOrderPos = IncOrderPosNext(&batch);
    debit.strAccount = strFrom;
    debit.nCreditDebit = -nAmount;
    debit.nTime = nNow;
    debit.strOtherAccount = strTo;
    debit.strComment = strComment;
    AddAccountingEntry(debit, &batch);
    
    CAccountingEntry credit;
    credit.nOrderPos = IncOrderPosNext(&batch);
    credit.strAccount = strTo;
    credit.nCreditDebit = nAmount;
    credit.nTime = nNow;
    credit.strOtherAccount = strFrom;
    credit.strComment = strComment;
    AddAccountingEntry(credit, &batch);
    if (!batch.TxnCommit())
        return false;
    return true;
}
bool CWallet::GetLabelDestination(CTxDestination &dest, const std::string& label, bool bForceNew)