Some metadata files are handled before MFT. This adds a null pointer
check for some corner cases that could lead to NPD while reading these
metadata files for a malformed NTFS image.
Signed-off-by: Edward Lo <edward.lo@ambergroup.io> Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com> Signed-off-by: Sasha Levin <sashal@kernel.org>