<!-- 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.
filtered_address = DecodeDestination(params[3].get_str());
        has_filtered_address = true;
    }
    
    std::map<CTxDestination, tallyitem> mapTally;
    for (const std::pair<const uint256, CWalletTx>& pairWtx : pwallet->mapWallet) {
        const CWalletTx& wtx = pairWtx.second;
        if (wtx.IsCoinBase() || !CheckFinalTx(*wtx.tx))
            continue;
        int nDepth = wtx.GetDepthInMainChain();
        if (nDepth < nMinDepth)
            continue;
        for (const CTxOut& txout : wtx.tx->vout)
        {
            CTxDestination address;
            if (!ExtractDestination(txout.scriptPubKey, address))
                continue;
            if (has_filtered_address && !(filtered_address == address)) {
                continue;
            }
            isminefilter mine = IsMine(*pwallet, address);
            if(!(mine & filter))
                continue;
            tallyitem& item = mapTally[address];
            item.nAmount += txout.nValue;
            item.nConf = std::min(item.nConf, nDepth);
            item.txids.push_back(wtx.GetHash());
            if (mine & ISMINE_WATCH_ONLY)
                item.fIsWatchonly = true;
        }