<!-- 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.
},
            true, true);
        if (options.exists("changeAddress")) {
            CTxDestination dest = DecodeDestination(options["changeAddress"].get_str());
            if (!IsValidDestination(dest)) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "changeAddress must be a valid bitcoin address");
            }
            coinControl.destChange = dest;
        }
        if (options.exists("changePosition"))
            change_position = options["changePosition"].get_int();
        if (options.exists("change_type")) {
            if (options.exists("changeAddress")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both changeAddress and address_type options");
            }
            coinControl.m_change_type = pwallet->m_default_change_type;
            if (!ParseOutputType(options["change_type"].get_str(), *coinControl.m_change_type)) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown change type '%s'", options["change_type"].get_str()));
            }
        }
        if (options.exists("includeWatching"))
            coinControl.fAllowWatchOnly = options["includeWatching"].get_bool();
        if (options.exists("lockUnspents"))
            lockUnspents = options["lockUnspents"].get_bool();
        if (options.exists("feeRate"))
        {
            coinControl.m_feerate = CFeeRate(AmountFromValue(options["feeRate"]));
            coinControl.fOverrideFeeRate = true;
        }
        if (options.exists("subtractFeeFromOutputs"))