The first commit ensures IsectBoxes are not set up unless
they are valid.
The second commit renames
`drw_bounds_are_valid` to `drw_bounds_corners_are_valid`,
and `drw_bounds_culling_enabled` to `drw_bounds_are_valid`
so it's harder to set up an invalid `IsectBox` by mistake.
(Continuation of #127807)
Pull Request: https://projects.blender.org/blender/blender/pulls/128125