<!-- 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.
subtractFeeFromOutputs = options["subtractFeeFromOutputs"].get_array();
        if (options.exists("replaceable")) {
            coinControl.m_signal_bip125_rbf = options["replaceable"].get_bool();
        }
        if (options.exists("conf_target")) {
            if (options.exists("feeRate")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both conf_target and feeRate");
            }
            coinControl.m_confirm_target = ParseConfirmTarget(options["conf_target"]);
        }
        if (options.exists("estimate_mode")) {
            if (options.exists("feeRate")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both estimate_mode and feeRate");
            }
            if (!FeeModeFromString(options["estimate_mode"].get_str(), coinControl.m_fee_mode)) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid estimate_mode parameter");
            }
        }
      }
    }
    if (tx.vout.size() == 0)
        throw JSONRPCError(RPC_INVALID_PARAMETER, "TX must have at least one output");
    if (change_position != -1 && (change_position < 0 || (unsigned int)change_position > tx.vout.size()))
        throw JSONRPCError(RPC_INVALID_PARAMETER, "changePosition out of bounds");
    for (unsigned int idx = 0; idx < subtractFeeFromOutputs.size(); idx++) {
        int pos = subtractFeeFromOutputs[idx].get_int();
        if (setSubtractFeeFromOutputs.count(pos))
            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid parameter, duplicated position: %d", pos));
        if (pos < 0)
            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid parameter, negative position: %d", pos));