<!-- 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.
break;
            case feebumper::Result::WALLET_ERROR:
                throw JSONRPCError(RPC_WALLET_ERROR, errors[0]);
                break;
            default:
                throw JSONRPCError(RPC_MISC_ERROR, errors[0]);
                break;
        }
    }
    
    if (!feebumper::SignTransaction(pwallet, mtx)) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Can't sign transaction.");
    }
    
    uint256 txid;
    if (feebumper::CommitTransaction(pwallet, hash, std::move(mtx), errors, txid) != feebumper::Result::OK) {
        throw JSONRPCError(RPC_WALLET_ERROR, errors[0]);
    }
    UniValue result(UniValue::VOBJ);
    result.pushKV("txid", txid.GetHex());
    result.pushKV("origfee", ValueFromAmount(old_fee));
    result.pushKV("fee", ValueFromAmount(new_fee));
    UniValue result_errors(UniValue::VARR);
    for (const std::string& error : errors) {
        result_errors.push_back(error);
    }
    result.pushKV("errors", result_errors);
    return result;
}
UniValue generate(const JSONRPCRequest& request)