transmogrify skips some membership rows causing foreign key errors

The group_members table in transmogrify uses the check_group_membership pre-row function to help process rows from the incoming cm_co_group_members table. That pre-row function throws an exception if both the owner and member fields are false, and the exception causes the entire row to be skipped and not put into the outgoing table. Later rows in the incoming table may refer to the skipped row using a foreign key because of ChangelogBehavior, and the missing target row in the outgoing table causes an error and a valid membership may be dropped.