dirstats: fix incorrect detection of nearest-neighbour angles large than 90°
dirstats: fix incorrect detection of nearest-neighbour angles large than 90°

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