<!-- 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.
{
public:
    CWallet * const pwallet;
    void ProcessSubScript(const CScript& subscript, UniValue& obj, bool include_addresses = false) const
    {
        
        std::vector<std::vector<unsigned char>> solutions_data;
        txnouttype which_type = Solver(subscript, solutions_data);
        obj.pushKV("script", GetTxnOutputType(which_type));
        obj.pushKV("hex", HexStr(subscript.begin(), subscript.end()));
        CTxDestination embedded;
        UniValue a(UniValue::VARR);
        if (ExtractDestination(subscript, embedded)) {