Ensure RGB32 images are not converted on upload to atlas.

Fixes "Typo No.12" reported at http://www.viva64.com/en/b/0251/

Change-Id: Ifa4d57df68b9515c76a8fb94f87d0a70ba3b5faf
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>