Code there was fairly naive and simple, missing some ID pointers,
sometimes improperly accessing non-ID data as IDs (usual dear Outliner
tree element usages of its 'ID' pointer...).
And code was especially quite severely broken in case these UI ID
usages were processed in a non-readonly context (i.e. if some of these
ID pointers were expected to be modified).
Code has been updated following existing very similar code in
`lib_link_workspace_layout_restore` from `readfile.cc`.
910f60de4c