@Override
	public void windowIconified( WindowEvent e ) {
		cancelPopupMenu();
	}
Cancels (hides) popup menus on Linux.
<p>
On Linux, popups are not hidden under following conditions, which results in
misplaced popups:
<ul>
  <li>window moved or resized
  <li>window maximized or restored
  <li>window iconified
  <li>window deactivated (e.g. activated other application)
</ul>

On Windows and macOS, popups are automatically hidden.
<p>
The implementation is similar to what's done in
{@code javax.swing.plaf.basic.BasicPopupMenuUI.MouseGrabber},
but only hides popup in some conditions.

@author Karl Tauber
flatlaf-core/src/main/java/com/formdev/flatlaf/LinuxPopupMenuCanceler.java