DICOM: fix sorting in odd cases where there is no change in acq number
DICOM: fix sorting in odd cases where there is no change in acq number

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