BUG: fixed bug in case the user asked for vertebral levels that are not available in the input image
BUG: fixed bug in case the user asked for vertebral levels that are not available in the input image

3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox