mtlognorm: Fixing convergence criterion bug when computing scale normalisation factors
mtlognorm: Fixing convergence criterion bug when computing scale normalisation factors

* Make sure we compare prev_mask to current mask before we cache the current mask. Genius!

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