BUG: fixed small bug on sct_label_utils
BUG: fixed small bug on sct_label_utils

Former-commit-id: 9f77958da432ba1f7530f7d64e068c2eb7a44551
Former-commit-id: b54fcfa13800d7229e6fe16557296dbaf7f6bbef
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox