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 :-)
nOrderPos += nOrderPosOff;
            nOrderPosNext = std::max(nOrderPosNext, nOrderPos + 1);
            if (!nOrderPosOff)
                continue;
            
            if (pwtx)
            {
                if (!batch.WriteTx(*pwtx))
                    return DBErrors::LOAD_FAIL;
            }
            else
                if (!batch.WriteAccountingEntry(pacentry->nEntryNo, *pacentry))
                    return DBErrors::LOAD_FAIL;
        }
    }
    batch.WriteOrderPosNext(nOrderPosNext);
    return DBErrors::LOAD_OK;
}
int64_t CWallet::IncOrderPosNext(WalletBatch *batch)
{
    AssertLockHeld(cs_wallet); 
    int64_t nRet = nOrderPosNext++;
    if (batch) {
        batch->WriteOrderPosNext(nOrderPosNext);
    } else {
        WalletBatch(*database).WriteOrderPosNext(nOrderPosNext);
    }
    return nRet;
}
bool CWallet::AccountMove(std::string strFrom, std::string strTo, CAmount nAmount, std::string strComment)