Bugfix: Process scans that have *no* value for PhantomMissingOverride
Bugfix: Process scans that have *no* value for PhantomMissingOverride

Since scans have no PhantomMissingOverride value by default, this
omitted many scans from check_phantom_scans.

sibis-platform/ncanda-data-integration,sibis-platform/ncanda-data-integration