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_wallet); 
    
    
    
    bool needsDB = !encrypted_batch;
    if (needsDB) {
        encrypted_batch = &batch;
    }
    if (!CCryptoKeyStore::AddKeyPubKey(secret, pubkey)) {
        if (needsDB) encrypted_batch = nullptr;
        return false;
    }
    if (needsDB) encrypted_batch = nullptr;
    
    CScript script;
    script = GetScriptForDestination(pubkey.GetID());
    if (HaveWatchOnly(script)) {
        RemoveWatchOnly(script);
    }
    script = GetScriptForRawPubKey(pubkey);
    if (HaveWatchOnly(script)) {
        RemoveWatchOnly(script);
    }
    if (!IsCrypted()) {
        return batch.WriteKey(pubkey,
                                                 secret.GetPrivKey(),
                                                 mapKeyMetadata[pubkey.GetID()]);
    }
    return true;