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 :-)
{
    AssertLockHeld(cs_main);
    AssertLockHeld(cs_wallet);
    vCoins.clear();
    CAmount nTotal = 0;
    for (const auto& entry : mapWallet)
    {
        const uint256& wtxid = entry.first;
        const CWalletTx* pcoin = &entry.second;
        if (!CheckFinalTx(*pcoin->tx))
            continue;
        if (pcoin->IsCoinBase() && pcoin->GetBlocksToMaturity() > 0)
            continue;
        int nDepth = pcoin->GetDepthInMainChain();
        if (nDepth < 0)
            continue;
        
        
        if (nDepth == 0 && !pcoin->InMempool())
            continue;
        bool safeTx = pcoin->IsTrusted();