BUG: fixed CSA computation. Fixed #989
BUG: fixed CSA computation. Fixed #989

Former-commit-id: 4fd59d32c9fdd817bb936a8fec372f2de8c8acea [formerly fde925461330f9f5f59e13d405400e4013e95b16]
Former-commit-id: da73ccb1aab791d1e680f4d0085a1fe071ea302a
Former-commit-id: 03549df385cb072d561cf04a1b1fac4b90dcf18a
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox