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 :-)
txByTime.insert(std::make_pair(entry.nTime, TxPair(nullptr, &entry)));
    }
    nOrderPosNext = 0;
    std::vector<int64_t> nOrderPosOffsets;
    for (TxItems::iterator it = txByTime.begin(); it != txByTime.end(); ++it)
    {
        CWalletTx *const pwtx = (*it).second.first;
        CAccountingEntry *const pacentry = (*it).second.second;
        int64_t& nOrderPos = (pwtx != nullptr) ? pwtx->nOrderPos : pacentry->nOrderPos;
        if (nOrderPos == -1)
        {
            nOrderPos = nOrderPosNext++;
            nOrderPosOffsets.push_back(nOrderPos);
            if (pwtx)
            {
                if (!batch.WriteTx(*pwtx))
                    return DBErrors::LOAD_FAIL;
            }
            else
                if (!batch.WriteAccountingEntry(pacentry->nEntryNo, *pacentry))
                    return DBErrors::LOAD_FAIL;
        }
        else
        {
            int64_t nOrderPosOff = 0;
            for (const int64_t& nOffsetStart : nOrderPosOffsets)
            {
                if (nOrderPos >= nOffsetStart)
                    ++nOrderPosOff;
            }