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 :-)
while (!todo.empty()) {
        uint256 now = *todo.begin();
        todo.erase(now);
        done.insert(now);
        auto it = mapWallet.find(now);
        assert(it != mapWallet.end());
        CWalletTx& wtx = it->second;
        int currentconfirm = wtx.GetDepthInMainChain();
        if (conflictconfirms < currentconfirm) {
            
            
            wtx.nIndex = -1;
            wtx.hashBlock = hashBlock;
            wtx.MarkDirty();
            batch.WriteTx(wtx);
            
            TxSpends::const_iterator iter = mapTxSpends.lower_bound(COutPoint(now, 0));
            while (iter != mapTxSpends.end() && iter->first.hash == now) {
                 if (!done.count(iter->second)) {
                     todo.insert(iter->second);
                 }
                 iter++;
            }
            
            
            MarkInputsDirty(wtx.tx);
        }
    }
}
void CWallet::SyncTransaction(const CTransactionRef& ptx, const CBlockIndex *pindex, int posInBlock, bool update_tx) {