Fix reading palette images in DDS handler.

Change-Id: I039a5f3376a8ebe7230f30a0df31c4a355f22349
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Alex Char <prevedtest@gmail.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>