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 :-)
{
    const CTransaction& tx = *ptx;
    {
        AssertLockHeld(cs_wallet);
        if (pIndex != nullptr) {
            for (const CTxIn& txin : tx.vin) {
                std::pair<TxSpends::const_iterator, TxSpends::const_iterator> range = mapTxSpends.equal_range(txin.prevout);
                while (range.first != range.second) {
                    if (range.first->second != tx.GetHash()) {
                        LogPrintf("Transaction %s (in block %s) conflicts with wallet transaction %s (both spend %s:%i)\n", tx.GetHash().ToString(), pIndex->GetBlockHash().ToString(), range.first->second.ToString(), range.first->first.hash.ToString(), range.first->first.n);
                        MarkConflicted(pIndex->GetBlockHash(), range.first->second);
                    }
                    range.first++;
                }
            }
        }
        bool fExisted = mapWallet.count(tx.GetHash()) != 0;
        if (fExisted && !fUpdate) return false;
        if (fExisted || IsMine(tx) || IsFromMe(tx))
        {
            /* Check if any keys in the wallet keypool that were supposed to be unused
             * have appeared in a new transaction. If so, remove those keys from the keypool.
             * This can happen when restoring an old wallet backup that does not contain
             * the mostly recently created transactions from newer versions of the wallet.
             */
            
            for (const CTxOut& txout: tx.vout) {