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
if (control == null || control.isDisposed()) {
			return;
		}
		Rectangle rect = getDecorationRectangle(control.getShell());
		
		
		
		if (previousDecorationRectangle != null) {
			rect = rect.union(previousDecorationRectangle);
		}
		
		control.getShell()
				.redraw(rect.x, rect.y, rect.width, rect.height, true);
		control.getShell().update();
		if (hover != null && getDescriptionText() != null) {
			hover.setText(getDescriptionText(), getDecorationRectangle(control
					.getParent()), control);
		}
		previousDecorationRectangle = null;
	}
	/*
	 * Show the specified text in the hover, positioning the hover near the
	 * specified control.
	 */
	private void showHoverText(String text, Control hoverNear) {
		
		if (!showHover) {
			return;
		}