ignore garbage values for all_site_admin_account_users_copies

Change-Id: Idc7b3cfceda71c73f8aefcc17bdaabc00de65ba5
Reviewed-on: https://gerrit.instructure.com/39913
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>