HPCC-11339 WsWorkunits should respect compulsory flag

Compulsory flag applies to initial superfile lookup, not to subfiles

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5990 from richardkchapman/esp-compulsory

HPCC-11339 WsWorkunits should respect compulsory flag

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>