<!-- 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.
{
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2) {
        throw std::runtime_error(
            "createwallet \"wallet_name\" ( disable_private_keys )\n"
            "\nCreates and loads a new wallet.\n"
            "\nArguments:\n"
            "1. \"wallet_name\"          (string, required) The name for the new wallet. If this is a path, the wallet will be created at the path location.\n"
            "2. disable_private_keys   (boolean, optional, default: false) Disable the possibility of private keys (only watchonlys are possible in this mode).\n"
            "\nResult:\n"
            "{\n"
            "  \"name\" :    <wallet_name>,        (string) The wallet name if created successfully. If the wallet was created using a full path, the wallet_name will be the full path.\n"
            "  \"warning\" : <warning>,            (string) Warning message if wallet was not loaded cleanly.\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("createwallet", "\"testwallet\"")
            + HelpExampleRpc("createwallet", "\"testwallet\"")
        );
    }
    std::string wallet_name = request.params[0].get_str();
    std::string error;
    std::string warning;
    bool disable_privatekeys = false;
    if (!request.params[1].isNull()) {
        disable_privatekeys = request.params[1].get_bool();
    }
    fs::path wallet_path = fs::absolute(wallet_name, GetWalletDir());
    if (fs::symlink_status(wallet_path).type() != fs::file_not_found) {