message: Fix scroller in `Scrollable` always being drawn
  ... instead of only drawing it when the mouse is over the `Scrollable`.
diff: @@ -714,9 +714,8 @@ pub fn draw<Renderer>(
  );
  }
  - if is_mouse_over
  - || state.is_scroller_grabbed()
  - || is_scrollbar_visible
  + if (is_mouse_over || state.is_scroller_grabbed())
  + && is_scrollbar_visible
  {
  renderer.fill_quad(
  renderer::Quad {
  