OPT: address the case of problematic segmentations (e.g., non continuous segmentation can occur at the extremities) --> the program display a warning but doesn't crash (fix issue #694).
OPT: address the case of problematic segmentations (e.g., non continuous segmentation can occur at the extremities) --> the program display a warning but doesn't crash (fix issue #694).

Former-commit-id: 79b7f7e004cfb611dd1349d0d652efb09111f6d3 [formerly eb8dd71dd27c1fc7aee0930e446c6f7fc4b01fa4]
Former-commit-id: dd46cd7e59e20b4041b101729f82f630f09903af
Former-commit-id: d13c4e874ae04c3076cf69fe9977d7f94ef1c16e
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox