#135476 – Fix #135441: integer overflow with large displacement modifier image – blender

The offset calculation would overflow inside ibuf_get_color given the
incoming arguments and image size.

Another similar problem, found from quick inspection, would occur inside
ibuf_get_color_clip as well.

The offset calculation would overflow inside `ibuf_get_color` given the
incoming arguments and image size.

Another similar problem, found from quick inspection, would occur inside
`ibuf_get_color_clip` as well.