nilfs2: fix NULL pointer dereference at nilfsbmaplookupatlevel()
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.9.331 by commit bb63454b66f4a73d4b267fd5061aaf3a5657172c. For more details please see the references link.