BUG: fix bug that can occur with some data (e.g., label/template/MNI-Poly-AMU_WM.nii.gz)
BUG: fix bug that can occur with some data (e.g., label/template/MNI-Poly-AMU_WM.nii.gz)

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