qt: Revert 7fa91e8312 partially

The AskPassphraseDialog modal dialog must be synchronous here as
expected in the WalletModel::requestUnlock() function.

Fixed an introduced regression.

src/qt/walletview.cpp

@@ -242,9 +242,11 @@ void WalletView::unlockWallet()
 {
     // Unlock wallet when requested by wallet model
     if (walletModel->getEncryptionStatus() == WalletModel::Locked) {
-        auto dlg = new AskPassphraseDialog(AskPassphraseDialog::Unlock, this);
-        dlg->setModel(walletModel);
-        GUIUtil::ShowModalDialogAndDeleteOnClose(dlg);
+        AskPassphraseDialog dlg(AskPassphraseDialog::Unlock, this);
+        dlg.setModel(walletModel);
+        // A modal dialog must be synchronous here as expected
+        // in the WalletModel::requestUnlock() function.
+        dlg.exec();
     }
 }