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::list<COutputEntry>& listSent, CAmount& nFee, std::string& strSentAccount, const isminefilter& filter) const
{
    nFee = 0;
    listReceived.clear();
    listSent.clear();
    strSentAccount = strFromAccount;
    
    CAmount nDebit = GetDebit(filter);
    if (nDebit > 0) 
    {
        CAmount nValueOut = tx->GetValueOut();
        nFee = nDebit - nValueOut;
    }
    
    for (unsigned int i = 0; i < tx->vout.size(); ++i)
    {
        const CTxOut& txout = tx->vout[i];
        isminetype fIsMine = pwallet->IsMine(txout);
        
        
        
        if (nDebit > 0)
        {
            
            if (pwallet->IsChange(txout))