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 v5.4.218 by commit 792211333ad77fcea50a44bb7f695783159fc63c. For more details please see the references link.