title: Prevent radio buttons resetting after push button has been clicked
body: <p>I've got a custom Dialog which contains two SWT.RADIO buttons and one SWT.PUSH button (opens a FileDialog). After I clicked the the second SWT.RADIO Button, clicked the SWT.PUSH button and returned from the FileDialog, the SWT.RADIO buttons are reset to their default selection.</p>
  
  <p>How can I prevent that?</p>
  
  <p>Reproducable code:</p>
  
  <pre><code>import org.eclipse.swt.SWT;
  import org.eclipse.swt.events.SelectionAdapter;
  import org.eclipse.swt.events.SelectionEvent;
  import org.eclipse.swt.layout.GridData;
  import org.eclipse.swt.layout.GridLayout;
  import org.eclipse.swt.widgets.Button;
  import org.eclipse.swt.widgets.Composite;
  import org.eclipse.swt.widgets.Display;
  import org.eclipse.swt.widgets.FileDialog;
  import org.eclipse.swt.widgets.Shell;
  
  public class TestDialog {
  
      public static void main(String[] args) {
          final Display display = new Display();
  
          Shell shell = new Shell(display);
          shell.setBounds(30, 30, 300, 150);
  
          shell.setLayout(new GridLayout(1, false));
  
          Composite comp = new Composite(shell, SWT.NONE);
          comp.setLayout(new GridLayout(2, false));
  
          Button btnRadio1 = new Button(comp, SWT.RADIO);
          btnRadio1.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, false, 1, 1));
          btnRadio1.setText("Radio Button 1");
  
          Button btnRadio2 = new Button(comp, SWT.RADIO);
          btnRadio2.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true, 1, 1));
          btnRadio2.setText("Radio Button 2");
  
          Composite comp2 = new Composite(shell, SWT.NO_RADIO_GROUP);
          comp2.setLayout(new GridLayout(1, false));
  
          Button btnPush = new Button(comp2, SWT.NONE);
          btnPush.setText("Push Button");
          btnPush.addSelectionListener(new SelectionAdapter() {
              @Override
              public void widgetSelected(SelectionEvent e) {
                  super.widgetSelected(e);
                  FileDialog dirDialog = new FileDialog(shell);
                  dirDialog.open();
              }
          });
  
          shell.open();
          while (!shell.isDisposed()) {
              if (!display.readAndDispatch())
                  display.sleep();
          }
          display.dispose();
      }
  }
  </code></pre>