HPCC-12361 Assert error (hashtable not empty) from new statistics

Missing a releaseAll(), it seems.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
HPCC-12215 Roxie record counts missing from child queries

Create the stats gatherer sooner.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>