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 (!CheckFinalTx(*tx))
        return false;
    int nDepth = GetDepthInMainChain();
    if (nDepth >= 1)
        return true;
    if (nDepth < 0)
        return false;
    if (!pwallet->m_spend_zero_conf_change || !IsFromMe(ISMINE_ALL)) 
        return false;
    
    if (!InMempool())
        return false;
    
    for (const CTxIn& txin : tx->vin)
    {
        
        const CWalletTx* parent = pwallet->GetWalletTx(txin.prevout.hash);
        if (parent == nullptr)
            return false;
        const CTxOut& parentOut = parent->tx->vout[txin.prevout.n];
        if (pwallet->IsMine(parentOut) != ISMINE_SPENDABLE)
            return false;
    }
    return true;
}
bool CWalletTx::IsEquivalentTo(const CWalletTx& _tx) const