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 :-)
assert(!encrypted_batch);
        encrypted_batch = new WalletBatch(*database);
        if (!encrypted_batch->TxnBegin()) {
            delete encrypted_batch;
            encrypted_batch = nullptr;
            return false;
        }
        encrypted_batch->WriteMasterKey(nMasterKeyMaxID, kMasterKey);
        if (!EncryptKeys(_vMasterKey))
        {
            encrypted_batch->TxnAbort();
            delete encrypted_batch;
            
            
            assert(false);
        }
        
        SetMinVersion(FEATURE_WALLETCRYPT, encrypted_batch, true);
        if (!encrypted_batch->TxnCommit()) {
            delete encrypted_batch;
            
            
            assert(false);
        }
        delete encrypted_batch;
        encrypted_batch = nullptr;
        Lock();
        Unlock(strWalletPassphrase);
        
        if (IsHDEnabled()) {