message: Remove unnecessary isEmpty() check
  The checks on mHighlightIndex will already correctly handle any empty
  lists.
diff: @@ -165,8 +165,7 @@ void ListBox::sort()
  void ListBox::onMouseDown(EventHandler::MouseButton /*button*/, int x, int y)
  {
  - // Ignore if menu is empty or invisible
  - if (isEmpty() || !visible()) { return; }
  + if (!visible()) { return; }
  const auto point = NAS2D::Point{x, y};
  