The fact that this pointer may be either to a regular ID, or an embedded
one, without any way to tell it withour accessing the nodetree data,
makes it tricky to handle properly when such 'other ID' access is not
allowed. Here there can still be assumptions and heuristics based on
other data, but this remains fragile and really sub-optimal code.
Should not have any behavioral change in current code, but required for
replacing `blend_read_lib`/`blend_read_expand` by `foreach_id`
(#105666).
710b47fe7c