fixelcfestats: Fix segfault with use of -mask option
fixelcfestats: Fix segfault with use of -mask option

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