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 v5.10.148 by commit 3f840480e31495ce674db4a69912882b5ac083f2. For more details please see the references link.