tckedit: Fix 'output_step_size' field in Properties
tckedit: Fix 'output_step_size' field in Properties

As reported by Chris Steele.

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