fix: clear password field and error in showTxApproval

Clears #approve-tx-password value and hides #approve-tx-error when the
transaction approval view is shown, matching the pattern used in
showSignApproval and confirmTx.show.

Closes #85

src/popup/views/approval.js

@@ -254,6 +254,9 @@ function showTxApproval(details) {
         $("approve-tx-data-section").classList.add("hidden");
     }
 
+    $("approve-tx-password").value = "";
+    $("approve-tx-error").classList.add("hidden");
+
     showView("approve-tx");
 }