HPCC-10052 - Add missing stop in previous commit.

I think only side-effect was a warning on stop() from the
NWaySelect activity.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #4886 from jakesmith/hpcc-10052b

HPCC-10052 - Add missing stop in previous commit.

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>