<!-- 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::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() < 2 || request.params.size() > 5)
        throw std::runtime_error(
                            "walletcreatefundedpsbt [{\"txid\":\"id\",\"vout\":n},...] [{\"address\":amount},{\"data\":\"hex\"},...] ( locktime ) ( replaceable ) ( options bip32derivs )\n"
                            "\nCreates and funds a transaction in the Partially Signed Transaction format. Inputs will be added if supplied inputs are not enough\n"
                            "Implements the Creator and Updater roles.\n"
                            "\nArguments:\n"
                            "1. \"inputs\"                (array, required) A json array of json objects\n"
                            "     [\n"
                            "       {\n"
                            "         \"txid\":\"id\",      (string, required) The transaction id\n"
                            "         \"vout\":n,         (numeric, required) The output number\n"
                            "         \"sequence\":n      (numeric, optional) The sequence number\n"
                            "       } \n"
                            "       ,...\n"
                            "     ]\n"
                            "2. \"outputs\"               (array, required) a json array with outputs (key-value pairs)\n"
                            "   [\n"
                            "    {\n"
                            "      \"address\": x.xxx,    (obj, optional) A key-value pair. The key (string) is the bitcoin address, the value (float or string) is the amount in " + CURRENCY_UNIT + "\n"
                            "    },\n"
                            "    {\n"
                            "      \"data\": \"hex\"        (obj, optional) A key-value pair. The key must be \"data\", the value is hex encoded data\n"
                            "    }\n"