The mechanism to instance meshes when there are no modifiers did not take
into account that modifiers might get re-evaluated from an operator that
requests loop normals. Now check for that case and no longer use the
instance then.
In the future, a better solution may be to compute loop normals on demand
as is already done for poly and vertex normals, but that would be a big
change.
Differential Revision: https://developer.blender.org/D14579
be799749dc