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 :-)
private:
    const CKeyStore &keystore;
    std::vector<CKeyID> &vKeys;
public:
    CAffectedKeysVisitor(const CKeyStore &keystoreIn, std::vector<CKeyID> &vKeysIn) : keystore(keystoreIn), vKeys(vKeysIn) {}
    void Process(const CScript &script) {
        txnouttype type;
        std::vector<CTxDestination> vDest;
        int nRequired;
        if (ExtractDestinations(script, type, vDest, nRequired)) {
            for (const CTxDestination &dest : vDest)
                boost::apply_visitor(*this, dest);
        }
    }
    void operator()(const CKeyID &keyId) {
        if (keystore.HaveKey(keyId))
            vKeys.push_back(keyId);
    }
    void operator()(const CScriptID &scriptId) {
        CScript script;
        if (keystore.GetCScript(scriptId, script))
            Process(script);
    }
    void operator()(const WitnessV0ScriptHash& scriptID)