<!-- 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.
}
        if (by_label)
        {
            tallyitem& _item = label_tally[label];
            _item.nAmount += nAmount;
            _item.nConf = std::min(_item.nConf, nConf);
            _item.fIsWatchonly = fIsWatchonly;
        }
        else
        {
            UniValue obj(UniValue::VOBJ);
            if(fIsWatchonly)
                obj.pushKV("involvesWatchonly", true);
            obj.pushKV("address",       EncodeDestination(address));
            obj.pushKV("amount",        ValueFromAmount(nAmount));
            obj.pushKV("confirmations", (nConf == std::numeric_limits<int>::max() ? 0 : nConf));
            obj.pushKV("label", label);
            UniValue transactions(UniValue::VARR);
            if (it != mapTally.end())
            {
                for (const uint256& _item : (*it).second.txids)
                {
                    transactions.push_back(_item.GetHex());
                }
            }
            obj.pushKV("txids", transactions);
            ret.push_back(obj);
        }
    }
    if (by_label)