<!-- 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.
"    ]\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("getaddressinfo", "\"1PSSGeFHDnKNxiEyFrD1wcEaHr9hrQDDWc\"")
            + HelpExampleRpc("getaddressinfo", "\"1PSSGeFHDnKNxiEyFrD1wcEaHr9hrQDDWc\"")
        );
    }
    LOCK(pwallet->cs_wallet);
    UniValue ret(UniValue::VOBJ);
    CTxDestination dest = DecodeDestination(request.params[0].get_str());
    
    if (!IsValidDestination(dest)) {
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid address");
    }
    std::string currentAddress = EncodeDestination(dest);
    ret.pushKV("address", currentAddress);
    CScript scriptPubKey = GetScriptForDestination(dest);
    ret.pushKV("scriptPubKey", HexStr(scriptPubKey.begin(), scriptPubKey.end()));
    isminetype mine = IsMine(*pwallet, dest);
    ret.pushKV("ismine", bool(mine & ISMINE_SPENDABLE));
    ret.pushKV("iswatchonly", bool(mine & ISMINE_WATCH_ONLY));
    UniValue detail = DescribeWalletAddress(pwallet, dest);
    ret.pushKVs(detail);
    if (pwallet->mapAddressBook.count(dest)) {
        ret.pushKV("label", pwallet->mapAddressBook[dest].name);
    }
    const CKeyMetadata* meta = nullptr;
    CKeyID key_id = GetKeyForDestination(*pwallet, dest);
    if (!key_id.IsNull()) {
        auto it = pwallet->mapKeyMetadata.find(key_id);