<!-- 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 (destinations.size() && (!fValidAddress || !destinations.count(address)))
            continue;
        UniValue entry(UniValue::VOBJ);
        entry.pushKV("txid", out.tx->GetHash().GetHex());
        entry.pushKV("vout", out.i);
        if (fValidAddress) {
            entry.pushKV("address", EncodeDestination(address));
            auto i = pwallet->mapAddressBook.find(address);
            if (i != pwallet->mapAddressBook.end()) {
                entry.pushKV("label", i->second.name);
            }
            if (scriptPubKey.IsPayToScriptHash()) {
                const CScriptID& hash = boost::get<CScriptID>(address);
                CScript redeemScript;
                if (pwallet->GetCScript(hash, redeemScript)) {
                    entry.pushKV("redeemScript", HexStr(redeemScript.begin(), redeemScript.end()));
                }
            }
        }
        entry.pushKV("scriptPubKey", HexStr(scriptPubKey.begin(), scriptPubKey.end()));
        entry.pushKV("amount", ValueFromAmount(out.tx->tx->vout[out.i].nValue));
        entry.pushKV("confirmations", out.nDepth);
        entry.pushKV("spendable", out.fSpendable);
        entry.pushKV("solvable", out.fSolvable);
        entry.pushKV("safe", out.fSafe);
        results.push_back(entry);
    }
    return results;
}
void FundTransaction(CWallet* const pwallet, CMutableTransaction& tx, CAmount& fee_out, int& change_position, UniValue options)