It's possible that multiple custom data layers share the same underlying data.
This data is only written once (per data-block) currently. However, when reading
the data again, two separate `ImplicitSharingInfo` were constructed which
referenced the same underlying memory. The fix is to reuse previously created
`ImplicitSharingInfo` that manage the same data.
Pull Request: https://projects.blender.org/blender/blender/pulls/118991
cc891aa699