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 :-)
walletInstance->SetMinVersion(FEATURE_LATEST); 
        }
        else
            LogPrintf("Allowing wallet upgrade up to %i\n", nMaxVersion);
        if (nMaxVersion < walletInstance->GetVersion())
        {
            InitError(_("Cannot downgrade wallet"));
            return nullptr;
        }
        walletInstance->SetMaxVersion(nMaxVersion);
    }
    
    if (gArgs.GetBoolArg("-upgradewallet", false)) {
        LOCK(walletInstance->cs_wallet);
        
        int max_version = walletInstance->nWalletVersion;
        if (!walletInstance->CanSupportFeature(FEATURE_HD_SPLIT) && max_version >=FEATURE_HD_SPLIT && max_version < FEATURE_PRE_SPLIT_KEYPOOL) {
            InitError(_("Cannot upgrade a non HD split wallet without upgrading to support pre split keypool. Please use -upgradewallet=169900 or -upgradewallet with no version specified."));
            return nullptr;
        }
        bool hd_upgrade = false;
        bool split_upgrade = false;
        if (walletInstance->CanSupportFeature(FEATURE_HD) && !walletInstance->IsHDEnabled()) {
            LogPrintf("Upgrading wallet to HD\n");
            walletInstance->SetMinVersion(FEATURE_HD);
            
            CPubKey masterPubKey = walletInstance->GenerateNewSeed();
            walletInstance->SetHDSeed(masterPubKey);
            hd_upgrade = true;
        }