HPCC-9480 A GROUP ROLLUP was incorrectly marked as having grouped output.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4485 from ghalliday/issue9480

HPCC-9480 A GROUP ROLLUP was incorrectly marked as having grouped output...

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>