Fix (unreported) liboverride: incomplete hierarchy when root is not object/collection.

We do not (currently) consider other ID types as 'end points' justifying
to create an override hierarchy, however if the 'root' ID (i.e. the ID
the user selected as base to create the override) is not an object or
collection, we still want to check all of its dependencies.

This fixes e.g. if a material depends on another Empty object, and user
tries to hierarchy-override that material, its Empty dependency not
being overridden.

source/blender/blenkernel/intern/lib_override.cc

@@ -937,11 +937,6 @@ static void lib_override_linked_group_tag(LibOverrideGroupTagData *data)
     id_root->tag |= data->tag;
   }
 
-  /* Only objects and groups are currently considered as 'keys' in override hierarchies. */
-  if (!ELEM(GS(id_root->name), ID_OB, ID_GR)) {
-    return;
-  }
-
   /* Tag all collections and objects recursively. */
   lib_override_linked_group_tag_recursive(data);