BUG : fixed issue 'must cover all z slices'
BUG : fixed issue 'must cover all z slices'


Former-commit-id: 9feab391ff6185acd8594e7524643e4237cabb02
Former-commit-id: ca93bac0b3dfb9186a0820d523b124a03f5b0151
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox