GSD-2022-1002311 jfs: prevent NULL deref in diFree

jfs: prevent NULL deref in diFree 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 v4.19.238 by commit 2ef74e3e0089b6615ee124e1183746974c6bb561...