<!-- 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.
{
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    CCoinControl coinControl;
    change_position = -1;
    bool lockUnspents = false;
    UniValue subtractFeeFromOutputs;
    std::set<int> setSubtractFeeFromOutputs;
    if (!options.isNull()) {
      if (options.type() == UniValue::VBOOL) {
        
        coinControl.fAllowWatchOnly = options.get_bool();
      }
      else {
        RPCTypeCheckArgument(options, UniValue::VOBJ);
        RPCTypeCheckObj(options,
            {
                {"changeAddress", UniValueType(UniValue::VSTR)},
                {"changePosition", UniValueType(UniValue::VNUM)},
                {"change_type", UniValueType(UniValue::VSTR)},
                {"includeWatching", UniValueType(UniValue::VBOOL)},
                {"lockUnspents", UniValueType(UniValue::VBOOL)},
                {"feeRate", UniValueType()}, 
                {"subtractFeeFromOutputs", UniValueType(UniValue::VARR)},
                {"replaceable", UniValueType(UniValue::VBOOL)},
                {"conf_target", UniValueType(UniValue::VNUM)},
                {"estimate_mode", UniValueType(UniValue::VSTR)},