Currently, DICOM-zip fails with 400 if you have any non-DICOM data in your zip, while SI just ignores it. Let's update this so that DICOM-zip only throws the 400 if you have no DICOM data, otherwise, like SI, it just ignores non-DICOM files. This prevents a user from having to extract and recompress legacy data tarballs/zips that often include some sort of txt (or even old XNAT catalog) files.