OPT: label_vertebrae: fixed output flag issue
OPT: label_vertebrae: fixed output flag issue

Former-commit-id: 5ee62eeb79c665ffc14561a73ef2f9d43f36412e
Former-commit-id: f866daf77119c48af25b715a2de5a85d62db2eca
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox