tckdynamic map: Fix to work against new libraries
tckdynamic map: Fix to work against new libraries

Also changed the mean voxel statistic calculation to provide zeroes outside the brain rather than NANs.

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