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 :-)
}
        m_pool_key_to_index.erase(keypool.vchPubKey.GetID());
        LogPrintf("keypool reserve %d\n", nIndex);
    }
    return true;
}
void CWallet::KeepKey(int64_t nIndex)
{
    
    WalletBatch batch(*database);
    batch.ErasePool(nIndex);
    LogPrintf("keypool keep %d\n", nIndex);
}
void CWallet::ReturnKey(int64_t nIndex, bool fInternal, const CPubKey& pubkey)
{
    
    {
        LOCK(cs_wallet);
        if (fInternal) {
            setInternalKeyPool.insert(nIndex);
        } else if (!set_pre_split_keypool.empty()) {
            set_pre_split_keypool.insert(nIndex);
        } else {
            setExternalKeyPool.insert(nIndex);
        }
        m_pool_key_to_index[pubkey.GetID()] = nIndex;
    }
    LogPrintf("keypool return %d\n", nIndex);
}
bool CWallet::GetKeyFromPool(CPubKey& result, bool internal)