message: [example/picking] Use saturating subtraction to avoid crash
diff: @@ -209,7 +209,7 @@ fn main() {
  if let (Some(cursor), Some(&(ref picking_texture, _))) = (cursor_position, picking_attachments.as_ref()) {
  let read_target = glium::Rect {
  left: (cursor.0 - 1) as u32,
  - bottom: picking_texture.get_height().unwrap() - std::cmp::max(cursor.1 - 1, 0) as u32,
  + bottom: picking_texture.get_height().unwrap().saturating_sub(std::cmp::max(cursor.1 - 1, 0) as u32),
  width: 1,
  height: 1,
  };
  