BUG: fixed gm inversion to wm
BUG: fixed gm inversion to wm

Former-commit-id: 974a15df04816b8dfef8b6879941d6a92ad983a2 [formerly fac8f7860eb486aca11a467a3a523255e4f187bb]
Former-commit-id: 075290a53b55e33e735fa51fb9b2d13ece17f748
Former-commit-id: c16d39179aae0de0a8aa1cc1a6278aa0733bdcc8
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox