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 :-)
{
    mapTxSpends.insert(std::make_pair(outpoint, wtxid));
    setLockedCoins.erase(outpoint);
    std::pair<TxSpends::iterator, TxSpends::iterator> range;
    range = mapTxSpends.equal_range(outpoint);
    SyncMetaData(range);
}
void CWallet::AddToSpends(const uint256& wtxid)
{
    auto it = mapWallet.find(wtxid);
    assert(it != mapWallet.end());
    CWalletTx& thisTx = it->second;
    if (thisTx.IsCoinBase()) 
        return;
    for (const CTxIn& txin : thisTx.tx->vin)
        AddToSpends(txin.prevout, wtxid);
}
bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)