nbd: Fix NULL pointer in flush_workqueue
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 v5.12.5 by commit 54b78ba7e96e5fe1edb8054e375d31a6c0dc60dc, it was introduced in version v5.4 by commit e9e006f5fcf2bab59149cb38a48a4817c1b538b4. For more details please see the references link.