exiv2 cannot read the Exif data written after deleting all tags
1) Add an Exif tag to a JPEG image without metadata
2) Remove the tag with the exiv2 utility
3) exiv2 -pt will fail with an error indicating corrupted Exif metadata
ExifData::copy() returns a DataBuf containing only a TIFF header if there is no Exif data to write. This is then written to the JPEG Exif APP Segment.