hpcc-8930 Child graph could have missing progress data

If a child graph had no activity initialization data serialized
to it from the master, the 'initialized' field was not set, with
the consequence that no graph progress stats were serialized
from the slaves to the master for those child graphs

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #4078 from jakesmith/hpcc-8930

HPCC-8930 Child graph could have missing progress data

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>