Bug fix in mrmath when using -axis option
Bug fix in mrmath when using -axis option

Suspect this one has been there for a while, but was exposed by the changes to ThreadedLoop.
Bug reported by Ben Jeurissen.

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