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 :-)
}
bool CWallet::AddKeyPubKey(const CKey& secret, const CPubKey &pubkey)
{
    WalletBatch batch(*database);
    return CWallet::AddKeyPubKeyWithDB(batch, secret, pubkey);
}
bool CWallet::AddCryptedKey(const CPubKey &vchPubKey,
                            const std::vector<unsigned char> &vchCryptedSecret)
{
    if (!CCryptoKeyStore::AddCryptedKey(vchPubKey, vchCryptedSecret))
        return false;
    {
        LOCK(cs_wallet);
        if (encrypted_batch)
            return encrypted_batch->WriteCryptedKey(vchPubKey,
                                                        vchCryptedSecret,
                                                        mapKeyMetadata[vchPubKey.GetID()]);
        else
            return WalletBatch(*database).WriteCryptedKey(vchPubKey,
                                                            vchCryptedSecret,
                                                            mapKeyMetadata[vchPubKey.GetID()]);
    }
}
void CWallet::LoadKeyMetadata(const CKeyID& keyID, const CKeyMetadata &meta)
{
    AssertLockHeld(cs_wallet); 
    UpdateTimeFirstKey(meta.nCreateTime);
    mapKeyMetadata[keyID] = meta;
}
void CWallet::LoadScriptMetadata(const CScriptID& script_id, const CKeyMetadata &meta)