lz: More checks on image sizes

Extend sizes check also to decoding, actually the source data
decoding images should be less safe than encoding.
This avoids different integer overflows and buffer overflows.
To avoid potential issues images are limited to 1GB.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Christophe Fergeau <cfergeau@redhat.com>