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 :-)
}
                    break;
                }
            }
            int64_t blocktime = pindex->GetBlockTime();
            nTimeSmart = std::max(latestEntry, std::min(blocktime, latestNow));
        } else {
            LogPrintf("%s: found %s in block %s not in index\n", __func__, wtx.GetHash().ToString(), wtx.hashBlock.ToString());
        }
    }
    return nTimeSmart;
}
bool CWallet::AddDestData(const CTxDestination &dest, const std::string &key, const std::string &value)
{
    if (boost::get<CNoDestination>(&dest))
        return false;
    mapAddressBook[dest].destdata.insert(std::make_pair(key, value));
    return WalletBatch(*database).WriteDestData(EncodeDestination(dest), key, value);
}
bool CWallet::EraseDestData(const CTxDestination &dest, const std::string &key)
{
    if (!mapAddressBook[dest].destdata.erase(key))
        return false;
    return WalletBatch(*database).EraseDestData(EncodeDestination(dest), key);
}
void CWallet::LoadDestData(const CTxDestination &dest, const std::string &key, const std::string &value)
{
    mapAddressBook[dest].destdata.insert(std::make_pair(key, value));
}
bool CWallet::GetDestData(const CTxDestination &dest, const std::string &key, std::string *value) const