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
return false;
		}
		if (control == null || control.isDisposed() || getImage() == null) {
			return false;
		}
		if (!control.isVisible()) {
			return false;
		}
		if (showOnlyOnFocus) {
			return hasFocus;
		}
		return true;
	}
	/*
	 * If in debug mode, print info about adding the specified listener.
	 */
	private void printAddListener(Widget widget, String listenerType) {
		listenerInstalls++;
		if (DEBUG) {
			System.out
					.println("Added listener>>>" + listenerType + " to>>>" + widget); 
		}
	}
	/*
	 * If in debug mode, print info about adding the specified listener.
	 */
	private void printRemoveListener(Widget widget, String listenerType) {
		listenerInstalls--;
		if (DEBUG) {
			System.out