Fix bug in reading DICOMDIR files with non-image data sets.
Fix bug in reading DICOMDIR files with non-image data sets.

The code assumed that a Series could only contain Images, but there
are many data sets in DICOM that are not images.

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