<!-- 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.
"1. \"address_type\"           (string, optional) The address type to use. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\". Default is set by -changetype.\n"
            "\nResult:\n"
            "\"address\"    (string) The address\n"
            "\nExamples:\n"
            + HelpExampleCli("getrawchangeaddress", "")
            + HelpExampleRpc("getrawchangeaddress", "")
       );
    if (pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Error: Private keys are disabled for this wallet");
    }
    LOCK(pwallet->cs_wallet);
    if (!pwallet->IsLocked()) {
        pwallet->TopUpKeyPool();
    }
    OutputType output_type = pwallet->m_default_change_type != OutputType::CHANGE_AUTO ? pwallet->m_default_change_type : pwallet->m_default_address_type;
    if (!request.params[0].isNull()) {
        if (!ParseOutputType(request.params[0].get_str(), output_type)) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown address type '%s'", request.params[0].get_str()));
        }
    }
    CReserveKey reservekey(pwallet);
    CPubKey vchPubKey;
    if (!reservekey.GetReservedKey(vchPubKey, true))
        throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, "Error: Keypool ran out, please call keypoolrefill first");
    reservekey.KeepKey();
    pwallet->LearnRelatedScripts(vchPubKey, output_type);
    CTxDestination dest = GetDestinationForKey(vchPubKey, output_type);
    return EncodeDestination(dest);
}
static UniValue setlabel(const JSONRPCRequest& request)