<!-- 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("label", pwallet->mapAddressBook[s.destination].name);
            }
            entry.pushKV("vout", s.vout);
            entry.pushKV("fee", ValueFromAmount(-nFee));
            if (fLong)
                WalletTxToJSON(wtx, entry);
            entry.pushKV("abandoned", wtx.isAbandoned());
            ret.push_back(entry);
        }
    }
    
    if (listReceived.size() > 0 && wtx.GetDepthInMainChain() >= nMinDepth)
    {
        for (const COutputEntry& r : listReceived)
        {
            std::string label;
            if (pwallet->mapAddressBook.count(r.destination)) {
                label = pwallet->mapAddressBook[r.destination].name;
            }
            UniValue entry(UniValue::VOBJ);
            if (involvesWatchonly || (::IsMine(*pwallet, r.destination) & ISMINE_WATCH_ONLY)) {
                entry.pushKV("involvesWatchonly", true);
            }
            MaybePushAddress(entry, r.destination);
            if (wtx.IsCoinBase())
            {
                if (wtx.GetDepthInMainChain() < 1)
                    entry.pushKV("category", "orphan");
                else if (wtx.IsImmatureCoinBase())
                    entry.pushKV("category", "immature");