REF: msct_register: clean code
REF: msct_register: clean code

Former-commit-id: 7bd59f751c5ee081d4ee54ea9e1b24eff426113b [formerly e82e6d3afa66b205b4e1606be893be1e3bf3bad0]
Former-commit-id: bb8ab3eb6a1a35a707528037eb67cc45080200fb
Former-commit-id: 998876d1c84d3e97d4ca708f16665c8db430f6f6
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox