SkJpegCodec: Fix compound metadata index validation

The comment explaining the range check describes the check that should
have been performed.

Bug: skia:55173
Change-Id: I2fd6c528167b294d0beef63afbfb73b54b86a313
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/631099
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed