HPCC-8836 Core on stored dataset with child dictionary

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4005 from richardkchapman/child-dict-stored

HPCC-8836 Core on stored dataset with child dictionary

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>