HPCC-12511 Allow resizeRow() to shrink huge memory allocations

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6711 from ghalliday/issue12511

HPCC-12511 Allow resizeRow() to shrink huge memory allocations

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>