HPCC-8950 Control:activeQueries crashes a stand alone roxie server instance

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4089 from richardkchapman/roxie-activequeries

HPCC-8950 Control:activeQueries crashes a stand alone roxie server insta...

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>