MGH / MGZ: Robust read of metadata, omit write of metadata
MGH / MGZ: Robust read of metadata, omit write of metadata

See #952.

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