<!-- Describe the issue -->

When trying to sign a transaction in a encrypted wallet that is locked, version 0.16 would return the following error:

```"Please enter the wallet passphrase with walletpassphrase first."```

While doing exactly the same procedure against 0.17, the response is something like:

```json
"hex": "020000000183ac9cc1137c444f32356fb070ecba194c87a05e43674c06a55f5b1d0561eabc0000000000ffffffff0180626a94000000001600141875aa6ab19c2551c11759cf3e9f4dd7aa40bcf500000000",
       "complete": false,
       "errors": [
         {
           "txid": "bcea61051d5b5fa5064c67435ea0874c19baec70b06f35324f447c13c19cac83",
           "vout": 0,
           "witness": [
           ],
           "scriptSig": "",
           "sequence": 4294967295,
           "error": "Unable to sign input, invalid stack size (possibly missing key)"
         }
     ]

```

<!--- What behavior did you expect? -->

v0.17 should check if the wallet is locked before trying to sign the tx and return the same error as v0.16 for consistency reasons.
std::vector<CPubKey> pubkeys;
    for (unsigned int i = 0; i < keys_or_addrs.size(); ++i) {
        if (IsHex(keys_or_addrs[i].get_str()) && (keys_or_addrs[i].get_str().length() == 66 || keys_or_addrs[i].get_str().length() == 130)) {
            pubkeys.push_back(HexToPubKey(keys_or_addrs[i].get_str()));
        } else {
            pubkeys.push_back(AddrToPubKey(pwallet, keys_or_addrs[i].get_str()));
        }
    }
    OutputType output_type = pwallet->m_default_address_type;
    if (!request.params[3].isNull()) {
        if (!ParseOutputType(request.params[3].get_str(), output_type)) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown address type '%s'", request.params[3].get_str()));
        }
    }
    
    CScript inner = CreateMultisigRedeemscript(required, pubkeys);
    CTxDestination dest = AddAndGetDestinationForScript(*pwallet, inner, output_type);
    pwallet->SetAddressBook(dest, label, "send");
    UniValue result(UniValue::VOBJ);
    result.pushKV("address", EncodeDestination(dest));
    result.pushKV("redeemScript", HexStr(inner.begin(), inner.end()));
    return result;
}
class Witnessifier : public boost::static_visitor<bool>
{
public:
    CWallet * const pwallet;
    CTxDestination result;
    bool already_witness;
    explicit Witnessifier(CWallet *_pwallet) : pwallet(_pwallet), already_witness(false) {}