<!-- 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.
{
        entry.pushKV("blockhash", wtx.hashBlock.GetHex());
        entry.pushKV("blockindex", wtx.nIndex);
        entry.pushKV("blocktime", LookupBlockIndex(wtx.hashBlock)->GetBlockTime());
    } else {
        entry.pushKV("trusted", wtx.IsTrusted());
    }
    uint256 hash = wtx.GetHash();
    entry.pushKV("txid", hash.GetHex());
    UniValue conflicts(UniValue::VARR);
    for (const uint256& conflict : wtx.GetConflicts())
        conflicts.push_back(conflict.GetHex());
    entry.pushKV("walletconflicts", conflicts);
    entry.pushKV("time", wtx.GetTxTime());
    entry.pushKV("timereceived", (int64_t)wtx.nTimeReceived);
    
    std::string rbfStatus = "no";
    if (confirms <= 0) {
        LOCK(mempool.cs);
        RBFTransactionState rbfState = IsRBFOptIn(*wtx.tx, mempool);
        if (rbfState == RBFTransactionState::UNKNOWN)
            rbfStatus = "unknown";
        else if (rbfState == RBFTransactionState::REPLACEABLE_BIP125)
            rbfStatus = "yes";
    }
    entry.pushKV("bip125-replaceable", rbfStatus);
    for (const std::pair<const std::string, std::string>& item : wtx.mapValue)
        entry.pushKV(item.first, item.second);
}
static std::string LabelFromValue(const UniValue& value)