libblkid: Fix out of bounds reads on bad NTFS Master File Table

libblkid: Fix out of bounds reads on bad NTFS Master File Table

The NTFS prober does not validate certain fields in struct file_attribute,
and could attempt to read the disk label from outside the space allocated
for the Master File Table.  Perform the appropriate checks.

Note that one variable (attr_off) is now 64-bit, so a check for integer
overflow has been removed as unneeded/confusing.

Signed-off-by: Alden Tondettar <alden.tondettar@gmail.com>