BUG: fixed bug in coding (case where the metric value is 0 in an whole tract => warning instead of error quitting the program)
BUG: fixed bug in coding (case where the metric value is 0 in an whole tract => warning instead of error quitting the program)

3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox