Bug 294462 [FieldAssist] ControlDecoration#showHoverText doesn't check if the widget is visible
If the HOVER-Text is set on decoration of a widget which is invisible the Hover-Shell is still poping up because it doesn't check if the control is invisible make the Hover appearing somewhere on the screen.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ControlDecoration.java
* relative to the display. The <code>data</code> field will contain the
	 * decoration that received the event.
	 * </p>
	 * 
	 * @param listener
	 *            the listener which should be notified
	 * 
	 * @see org.eclipse.swt.events.MenuDetectListener
	 * @see org.eclipse.swt.events.MenuDetectEvent
	 * @see #removeMenuDetectListener
	 */
	public void addMenuDetectListener(MenuDetectListener listener) {
		menuDetectListeners.add(listener);
	}
	/**
	 * Removes the listener from the collection of listeners who will be
	 * notified when the platform-specific context menu trigger has occurred.
	 * 
	 * @param listener
	 *            the listener which should no longer be notified. This message
	 *            has no effect if the listener was not previously added to the
	 *            receiver.
	 * 
	 * @see org.eclipse.swt.events.MenuDetectListener
	 * @see #addMenuDetectListener
	 */
	public void removeMenuDetectListener(MenuDetectListener listener) {
		menuDetectListeners.remove(listener);
	}
	/**