Button types of a DialogPane are set twice, returns a wrong button

ADDITIONAL SYSTEM INFORMATION :
Windows 10
Jdk-11.0.2 with newest JavaFX sources
Jdk1.8.0_241

A DESCRIPTION OF THE PROBLEM :
When the button types of a DialogPane are set twice, DialogPane#lookupButton does return a wrong button.

This is due DialogPane adding two list change listeners to 'buttons' (#getButtonTypes). They have the wrong order, which will result in the button bar not changing at all, but the buttonNodes list will have a new button added to it, which will not be displayed.

I will file a PR showing (via testcase) and fixing the described bug.


---------- BEGIN SOURCE ----------
public class Test extends Application {

    @Override
    public void start(Stage primaryStage) {
        Scene scene = new Scene(new BorderPane());
        primaryStage.setScene(scene);

        primaryStage.show();

        Dialog dialog = new Dialog();
        dialog.getDialogPane().getButtonTypes().setAll(ButtonType.OK);
        dialog.getDialogPane().getButtonTypes().setAll(ButtonType.OK);

        Button node = (Button) dialog.getDialogPane().lookupButton(ButtonType.OK);
        node.setText("TEST");

        dialog.showAndWait();
        // The OK button won't show 'TEST'
    }

}
---------- END SOURCE ----------

FREQUENCY : always