<!-- 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.
"                           Those recipients will receive less bitcoins than you enter in their corresponding amount field.\n"
            "                           If no addresses are specified here, the sender pays the fee.\n"
            "    [\n"
            "      \"address\"          (string) Subtract fee from this address\n"
            "      ,...\n"
            "    ]\n"
            "6. replaceable            (boolean, optional) Allow this transaction to be replaced by a transaction with higher fees via BIP 125\n"
            "7. conf_target            (numeric, optional) Confirmation target (in blocks)\n"
            "8. \"estimate_mode\"      (string, optional, default=UNSET) The fee estimate mode, must be one of:\n"
            "       \"UNSET\"\n"
            "       \"ECONOMICAL\"\n"
            "       \"CONSERVATIVE\"\n"
             "\nResult:\n"
            "\"txid\"                   (string) The transaction id for the send. Only 1 transaction is created regardless of \n"
            "                                    the number of addresses.\n"
            "\nExamples:\n"
            "\nSend two amounts to two different addresses:\n"
            + HelpExampleCli("sendmany", "\"\" \"{\\\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\\\":0.01,\\\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\\\":0.02}\"") +
            "\nSend two amounts to two different addresses setting the confirmation and comment:\n"
            + HelpExampleCli("sendmany", "\"\" \"{\\\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\\\":0.01,\\\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\\\":0.02}\" 6 \"testing\"") +
            "\nSend two amounts to two different addresses, subtract fee from amount:\n"
            + HelpExampleCli("sendmany", "\"\" \"{\\\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\\\":0.01,\\\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\\\":0.02}\" 1 \"\" \"[\\\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\\\",\\\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\\\"]\"") +
            "\nAs a json rpc call\n"
            + HelpExampleRpc("sendmany", "\"\", {\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\":0.01,\"1353tsE8YMTA4EuV7dgUXGjNFf9KpVvKHz\":0.02}, 6, \"testing\"")
        );
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    LOCK2(cs_main, pwallet->cs_wallet);
    if (pwallet->GetBroadcastTransactions() && !g_connman) {