CVE-2025-40119 ext4: fix potential null deref in ext4_mb_init()

In the Linux kernel, the following vulnerability has been resolved: ext4: fix potential null deref in ext4mbinit In ext4mbinit, ext4mbavgfragmentsizedestroy may be called when sbi-smbavgfragmentsize remains uninitialized e.g., if groupinfo slab cache allocation fails. Since...