amcheck: Fix missing allequalimage corruption report

amcheck: Fix missing allequalimage corruption report

When amcheck validates that a B-Tree metapage's allequalimage flag
matches _bt_allequalimage(), it could fail to report corruption
unless one of the index key columns used interval_ops. As a result,
pg_amcheck could silently miss this corruption on other opclasses,
incorrectly reporting the index as valid.

The mistake was that bt_index_check_callback() kept ereport(ERROR)
inside the loop that scans key attributes for INTERVAL_BTREE_FAM_OID,
even though that loop is only needed to decide whether to add
the interval-specific hint. This commit moves ereport() out of the loop
so allequalimage mismatches are always reported, while still emitting
the hint for affected interval indexes.

Back-patch to v18, where d70b17636dd introduced this regression
while moving the check into bt_index_check_callback().

Author: Chao Li <lic@highgo.com>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/011ACC9C-CB87-4160-ACE7-4ED57AB86E15@gmail.com
Backpatch-through: 18