NILFS2 has up to 7 keys, per the data structure. Do not permit array
indices in excess of that.
This catches some OOB reads. I don't know how controllable the invalidly
read data is or if that could be used later in the program.
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>