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 :-)
{
    std::map<CTxDestination, CAmount> balances;
    {
        LOCK(cs_wallet);
        for (const auto& walletEntry : mapWallet)
        {
            const CWalletTx *pcoin = &walletEntry.second;
            if (!pcoin->IsTrusted())
                continue;
            if (pcoin->IsCoinBase() && pcoin->GetBlocksToMaturity() > 0)
                continue;
            int nDepth = pcoin->GetDepthInMainChain();
            if (nDepth < (pcoin->IsFromMe(ISMINE_ALL) ? 0 : 1))
                continue;
            for (unsigned int i = 0; i < pcoin->tx->vout.size(); i++)
            {
                CTxDestination addr;
                if (!IsMine(pcoin->tx->vout[i]))
                    continue;
                if(!ExtractDestination(pcoin->tx->vout[i].scriptPubKey, addr))
                    continue;
                CAmount n = IsSpent(walletEntry.first, i) ? 0 : pcoin->tx->vout[i].nValue;
                if (!balances.count(addr))
                    balances[addr] = 0;