It crashes :-D

However, that would mean that the user is trying to normalize a matrix with at least one column of zeroes. Note that it is close to happening in the Oasis example, where we actually need some workaround to exclude to voxels with a zero between-subject variance from the analysis.

The correction I propose is the following:
- We catch the design problem (i.e. column(s) of zeros) early
- We raise a warning
- We use a inner mask in order to perform the analysis on the remaining, correct columns
- We return the results with zeros where there were some initially (using the inner mask again).