fs/sfs: Check if allocated memory is NULL

fs/sfs: Check if allocated memory is NULL

When using grub_zalloc(), if we are out of memory, this function can fail.
After allocating memory, we should check if grub_zalloc() returns NULL.
If so, we should handle this error.

Fixes: CID 473856
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Gbp-Pq: Topic cve-2025-jan
Gbp-Pq: Name fs-sfs-Check-if-allocated-memory-is-NULL.patch