Better handle SOS CSi values and order

Image SOS CSi markers should be distinct. Enforce that constraint when
reading multiple CSi values in get_sos().

[email protected]
BUG=258723

Review URL: https://codereview.chromium.org/27117002

git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/libjpeg_turbo@228381 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
3 files changed