HPCC-9905 Fix problems with embeded functions returning datasets

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4776 from ghalliday/issue9905

HPCC-9905 Fix problems with embeded functions returning datasets

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>