A mistake in handling legacy checks for special 'idx_token' column
resulted in not recognizing materialized views backing secondary
indexes properly. The mistake is really a typo, but with bad
consequences - instead of checking the view schema for being an index,
we asked for the base schema, which is definitely not an index of
itself.
Branches 3.1,3.2 (asap)
Fixes#5621Fixes#4744
(cherry picked from commit 9b379e3d63)
c0253d9221