<!-- 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.
#include <amount.h>
#include <chain.h>
#include <consensus/validation.h>
#include <core_io.h>
#include <httpserver.h>
#include <validation.h>
#include <key_io.h>
#include <net.h>
#include <outputtype.h>
#include <policy/feerate.h>
#include <policy/fees.h>
#include <policy/policy.h>
#include <policy/rbf.h>
#include <rpc/mining.h>
#include <rpc/rawtransaction.h>
#include <rpc/server.h>
#include <rpc/util.h>
#include <script/sign.h>
#include <shutdown.h>
#include <timedata.h>
#include <util.h>
#include <utilmoneystr.h>
#include <wallet/coincontrol.h>