fixelcfestats: Various fixels for -mask option
fixelcfestats: Various fixels for -mask option

Also includes a bug fix where opting to not smooth the input data would likely have resulted in an error.

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3