Blender Git Loki

Fix T74983: Material preview icons don't refresh

The root cause of the issue reported in T74983 is that an `IDNode` would
not be marked as user-modified. This marking happened while looping over
outgoing relations of one of its operation nodes. Since rBff60dd8b18ed
unused relations are removed, and as a result the `IDNode` would not be
marked.

The solution was to move the responsible code outside the loop; this is
probably a good idea anyway, as the code did not actually use the
looped-over relations at all, and was thus repeated unnecessarily.