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);
        CWalletTx wtxNew(this, std::move(tx));
        wtxNew.mapValue = std::move(mapValue);
        wtxNew.vOrderForm = std::move(orderForm);
        wtxNew.strFromAccount = std::move(fromAccount);
        wtxNew.fTimeReceivedIsTxTime = true;
        wtxNew.fFromMe = true;
        LogPrintf("CommitTransaction:\n%s", wtxNew.tx->ToString()); 
        {
            
            reservekey.KeepKey();
            
            
            AddToWallet(wtxNew);
            
            for (const CTxIn& txin : wtxNew.tx->vin)
            {
                CWalletTx &coin = mapWallet.at(txin.prevout.hash);
                coin.BindWallet(this);
                NotifyTransactionChanged(this, coin.GetHash(), CT_UPDATED);
            }
        }
        
        
        CWalletTx& wtx = mapWallet.at(wtxNew.GetHash());
        if (fBroadcastTransactions)
        {