Commit e7eea52b has introduced a new function
RelationGetIdentityKeyBitmap which omits to handle the case where there is
no replica identity index on a relation.

Author: Mark Dilger
Reviewed-by: Takamichi Osumi, Amit Kapila
Discussion: https://www.postgresql.org/message-id/4C99A862-69C8-431F-960A-81B1151F1B89@enterprisedb.com