Use a non-zero NPGTHRSH setting for better access paths when statistics show empty tables or defaults

(Terry Purcell and Paul McWilliams) Db2 12 improves how the Db2 optimizer uses the NPGTHRSH subsystem parameter for default statistics. However, we’ve found that very few clients are even familiar with the NPGTHRSH subsystem parameter, and the current default value disables its function.