CVE-2026-64431 ntfs: avoid calling post_write_mst_fixup() for invalid index_block

In the Linux kernel, the following vulnerability has been resolved: ntfs: avoid calling postwritemstfixup for invalid indexblock ntfsicxibsyncwrite calls postwritemstfixup when ntfsibwrite returns an error, intending to restore the buffer after a failed write. However, ntfsibwrite returns an erro...