<!-- 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.
}
    std::string wallet_name;
    if (GetWalletNameFromJSONRPCRequest(request, wallet_name)) {
        if (!request.params[0].isNull()) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot unload the requested wallet");
        }
    } else {
        wallet_name = request.params[0].get_str();
    }
    std::shared_ptr<CWallet> wallet = GetWallet(wallet_name);
    if (!wallet) {
        throw JSONRPCError(RPC_WALLET_NOT_FOUND, "Requested wallet does not exist or is not loaded");
    }
    
    
    
    if (!RemoveWallet(wallet)) {
        throw JSONRPCError(RPC_MISC_ERROR, "Requested wallet already unloaded");
    }
    UnregisterValidationInterface(wallet.get());
    
    
    
    wallet->NotifyUnload();
    
    
    
    return NullUniValue;
}
static UniValue resendwallettransactions(const JSONRPCRequest& request)