<!-- 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"
            "\nExamples:\n"
            "\nList the most recent 10 transactions in the systems\n"
            + HelpExampleCli("listtransactions", "") +
            "\nList transactions 100 to 120\n"
            + HelpExampleCli("listtransactions", "\"*\" 20 100") +
            "\nAs a json rpc call\n"
            + HelpExampleRpc("listtransactions", "\"*\", 20, 100")
        );
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    if (!request.params[0].isNull() && request.params[0].get_str() != "*") {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Dummy value must be set to \"*\"");
    }
    int nCount = 10;
    if (!request.params[1].isNull())
        nCount = request.params[1].get_int();
    int nFrom = 0;
    if (!request.params[2].isNull())
        nFrom = request.params[2].get_int();
    isminefilter filter = ISMINE_SPENDABLE;
    if(!request.params[3].isNull())
        if(request.params[3].get_bool())
            filter = filter | ISMINE_WATCH_ONLY;
    if (nCount < 0)
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Negative count");
    if (nFrom < 0)
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Negative from");
    UniValue ret(UniValue::VARR);