This fixes two things: The format detection, and a bug in `udif`.
First, by categorizing the `.dmg` extension as compressed image,
`.isSupportedImage()` would attempt to detect the format after stripping
the extension, causing it to be misdetected.
Second, `udif`'s ReadStream didn't add the `dataForkOffset` to its
position when reading blocks, causing the wrong data to be read for some images,
in turn causing zlib to error on invalid headers.
Changes:
- Classify `.dmg` as `type: 'image'`
- Update `udif` to 0.8.0
Change-Type: patch
Changelog-Entry: Fix Apple disk image detection & streaming
Signed-off-by: Juan Cruz Viotti <jviotti@openmailbox.org>
