NEW: GM segmentation: clean code. (void for now)
NEW: GM segmentation: clean code. (void for now)

Former-commit-id: 2d7e922741d1413bc6a9491e6c54fc1f1beba336
Former-commit-id: 3da6a9f1aa95bfc6c62f68cfb760c2ddfe55cd42
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox