BUG: fixed sct_flatten_sagittal about control points
BUG: fixed sct_flatten_sagittal about control points

Former-commit-id: 8819235f28deff607a1a1cb6d5bf4bfb0ba06156
Former-commit-id: 99a82f31ecd8848f4d0c82d51cb4df60c13d3e9c
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox