HPCC-11480 Make spilling streams, free pointer arrays asap

Spilling streams left the point arrays allocated, these can be
sizeable and cause fragmentation issues, free them asap on spill
event.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #5917 from jakesmith/hpcc-11480

HPCC-11480 Make spilling streams, free pointer arrays asap

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>