The lower texture levels (below the lod offset) aren't used and can't be seen, so don't count them in levelCount. BUG= Review URL: https://codereview.appspot.com/6492084 git-svn-id: https://angleproject.googlecode.com/svn/trunk@1275 736b8ea6-26fd-11df-bfd4-992fa37f6226
