Add a sanity check to the multi-stack check, avoid single-slice volumes.
Add a sanity check to the multi-stack check, avoid single-slice volumes.

hendradarwin/vtk-dicom,dgobbi/vtk-dicom,dgobbi/vtk-dicom,hendradarwin/vtk-dicom,dgobbi/vtk-dicom,hendradarwin/vtk-dicom