fix(Ledger): optimize terminal msg output

Author: lxcmyf

src/main/java/org/tron/ledger/listener/LedgerEventListener.java

@@ -1,6 +1,7 @@
 package org.tron.ledger.listener;
 
 import static org.tron.common.utils.TransactionUtils.getTransactionId;
+import static org.tron.common.utils.Utils.greenBoldHighlight;
 import static org.tron.ledger.console.ConsoleColor.ANSI_RED;
 import static org.tron.ledger.console.ConsoleColor.ANSI_RESET;
 import static org.tron.ledger.console.ConsoleColor.ANSI_YELLOW;
@@ -209,6 +210,7 @@ public void hidDataReceived(HidServicesEvent event) {
         doLedgerSignEnd();
       }
     }
+    System.out.println(greenBoldHighlight("Enter") + " to continue...");
   }
 
   private void doLedgerSignEnd() {

src/main/java/org/tron/walletserver/WalletApi.java

@@ -810,6 +810,10 @@ private Transaction signTransaction(Transaction transaction)
             return transaction;
           }
           HidDevice hidDevice = HidServicesWrapper.getInstance().getHidDevice(wf.getAddress(), getPath());
+          if (hidDevice == null) {
+            TransactionSignManager.getInstance().setTransaction(null);
+            return null;
+          }
           Optional<String> state = LedgerSignResult.getLastTransactionState(hidDevice.getPath());
           boolean confirmed = state.isPresent() && LedgerSignResult.SIGN_RESULT_SUCCESS.equals(state.get());
           if (weight.getResult().getCode() == response_code.NOT_ENOUGH_PERMISSION && confirmed) {