D12002: Check if group < LastGroup, as KIconEffect doesn't handle UserGroup anyway

[David Faure]

dfaure accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R302 KIconThemes

BRANCH
  fixWarning

REVISION DETAIL
  https://phabricator.kde.org/D12002

To: fabiank, mart, dfaure, mlaurent
Cc: #frameworks, michaelh, bruns