<!-- 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.
bool operator()(const CKeyID &keyID) {
        if (pwallet) {
            CScript basescript = GetScriptForDestination(keyID);
            CScript witscript = GetScriptForWitness(basescript);
            if (!IsSolvable(*pwallet, witscript)) {
                return false;
            }
            return ExtractDestination(witscript, result);
        }
        return false;
    }
    bool operator()(const CScriptID &scriptID) {
        CScript subscript;
        if (pwallet && pwallet->GetCScript(scriptID, subscript)) {
            int witnessversion;
            std::vector<unsigned char> witprog;
            if (subscript.IsWitnessProgram(witnessversion, witprog)) {
                ExtractDestination(subscript, result);
                already_witness = true;
                return true;
            }
            CScript witscript = GetScriptForWitness(subscript);
            if (!IsSolvable(*pwallet, witscript)) {
                return false;
            }
            return ExtractDestination(witscript, result);
        }
        return false;
    }
    bool operator()(const WitnessV0KeyHash& id)