fs/ntfs3: fix mount failure for sparse runs in run_unpack()

fs/ntfs3: fix mount failure for sparse runs in run_unpack()

Some NTFS volumes failed to mount because sparse data runs were not
handled correctly during runlist unpacking. The code performed arithmetic
on the special SPARSE_LCN64 marker, leading to invalid LCN values and
mount errors.

Add an explicit check for the case described above, marking the run as
sparse without applying arithmetic.

Fixes: 736fc7bf5f68 ("fs: ntfs3: Fix integer overflow in run_unpack()")
Cc: stable@vger.kernel.org
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>