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 :-)
FeeCalculation feeCalc;
    CAmount nFeeNeeded;
    int nBytes;
    {
        std::set<CInputCoin> setCoins;
        LOCK2(cs_main, cs_wallet);
        {
            std::vector<COutput> vAvailableCoins;
            AvailableCoins(vAvailableCoins, true, &coin_control);
            CoinSelectionParams coin_selection_params; 
            
            
            
            CScript scriptChange;
            
            if (!boost::get<CNoDestination>(&coin_control.destChange)) {
                scriptChange = GetScriptForDestination(coin_control.destChange);
            } else { 
                
                
                
                
                
                
                
                if (IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
                    strFailReason = _("Can't generate a change-address key. Private keys are disabled for this wallet.");
                    return false;
                }
                CPubKey vchPubKey;