Update SkCodec::rewindIfNeeded comment

Bug: skia:
Change-Id: I3c08535115b139be80341543daea6d5e23065cd0
Reviewed-on: https://skia-review.googlesource.com/146022
Reviewed-by: Leon Scroggins <scroggo@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>
1 file changed