HPCC-11618 Roxie core when detaching from dali

If roxie detaches from dali while a Workunit listener thread is at certain
locations inside dodequeue, Roxie may core.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6022 from richardkchapman/roxie-lockdali-core

HPCC-11618 Roxie core when detaching from dali

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>