tckgen: downsampler returns true for streamline lengths < 1
tckgen: downsampler returns true for streamline lengths < 1

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