HPCC-10411 - Catch out of bounds AddSuperFile @ pos

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #5149 from jakesmith/hpcc-10411

HPCC-10411 - Catch out of bounds AddSuperFile @ pos

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>