MDEV-9755: Buildbot shows a crash in JOIN::make_aggr_tables_info()
MDEV-9755: Buildbot shows a crash in JOIN::make_aggr_tables_info()

Don't attempt to do query pushdown when all tables have been optimized
away (tables_list=NULL)>

natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2