tck2connectome: Fix length quantification
tck2connectome: Fix length quantification

This was fixed in 2cbfa942 but re-introduced in 7f70bbfc.

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