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 (walletInstance->CanSupportFeature(FEATURE_HD_SPLIT)) {
            LogPrintf("Upgrading wallet to use HD chain split\n");
            walletInstance->SetMinVersion(FEATURE_PRE_SPLIT_KEYPOOL);
            split_upgrade = FEATURE_HD_SPLIT > prev_version;
        }
        
        if (split_upgrade) {
            walletInstance->MarkPreSplitKeys();
        }
        
        if (hd_upgrade) {
            if (!walletInstance->TopUpKeyPool()) {
                InitError(_("Unable to generate keys"));
                return nullptr;
            }
        }
    }
    if (fFirstRun)
    {
        
        if (!gArgs.GetBoolArg("-usehd", true)) {
            InitError(strprintf(_("Error creating %s: You can't create non-HD wallets with this version."), walletFile));
            return nullptr;
        }
        walletInstance->SetMinVersion(FEATURE_LATEST);
        if ((wallet_creation_flags & WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
            
            walletInstance->SetWalletFlag(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
        } else {