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 :-)
if (change_position->nValue >= MIN_FINAL_CHANGE + additionalFeeNeeded) {
                        change_position->nValue -= additionalFeeNeeded;
                        nFeeRet += additionalFeeNeeded;
                        break; 
                    }
                }
                
                
                if (nSubtractFeeFromAmount > 0) {
                    pick_new_inputs = false;
                }
                
                nFeeRet = nFeeNeeded;
                coin_selection_params.use_bnb = false;
                continue;
            }
        }
        if (nChangePosInOut == -1) reservekey.ReturnKey(); 
        
        txNew.vin.clear();
        std::vector<CInputCoin> selected_coins(setCoins.begin(), setCoins.end());
        std::shuffle(selected_coins.begin(), selected_coins.end(), FastRandomContext());