MRView tractogram tool: fix bug in lines render when thresholding
MRView tractogram tool: fix bug in lines render when thresholding

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