Top-level JFrame can be selected, top-level JDialog cannot

Nobody has claimed this yet.

I'm trying to understand why Robot Framework can't seem to connect when using a JDialog as the top level window but it works perfectly when using a JFrame.

The test:
```robot
*** Settings ***
Library RemoteSwingLibrary debug=True

*** Test Cases ***
My Test Case
Start Application DialogTest java -cp /projects/rdialog DialogTest
Select Dialog Main
Push Button Close
```

A minimal dialog example:
```java
import javax.swing.*;

public class DialogTest {
public static void main(String[] args) {
JButton button = new JButton("Close");
JDialog dialog = new JDialog();
dialog.setTitle("Main");
dialog.add(button);
dialog.setBounds(50, 50, 200, 100);
button.addActionListener(e -> {
dialog.dispose();
});
dialog.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
dialog.setVisible(true);
}
}
```
When attempting to run the test it fails with `RemoteSwingLibraryTimeoutError: Agent port not received before timeout`.
Running the test with `Select Window` instead of `Select Dialog` and replacing `JDialog` with `JFrame` in the source works. What am I missing here?

Start with the RemoteSwingLibrary handling behind Select Dialog and Select Window, then reproduce the issue using the provided Robot test and minimal DialogTest Java application. Done means a top-level JDialog connects without the Agent port timeout and the test can select Main and push Close.

Written by the indexing model from the issue text.