message: Move mHighlightIndex checks earlier
  These checks are cheap and likely to trigger early return, so should be
  done early.
diff: @@ -165,11 +165,11 @@ void ListBox::sort()
  void ListBox::onMouseDown(EventHandler::MouseButton /*button*/, int x, int y)
  {
  - if (!visible()) { return; }
  + if (!visible() || mHighlightIndex == constants::NO_SELECTION || mHighlightIndex >= mItems.size()) { return; }
  const auto point = NAS2D::Point{x, y};
  - if (!rect().contains(point) || mHighlightIndex == constants::NO_SELECTION)
  + if (!rect().contains(point))
  {
  return;
  }
  @@ -179,11 +179,6 @@ void ListBox::onMouseDown(EventHandler::MouseButton /*button*/, int x, int y)
  return; // if the mouse is on the slider then the slider should handle that
  }
  - if (mHighlightIndex >= mItems.size())
  - {
  - return;
  - }
  -
  setSelected(mHighlightIndex);
  }
  