fs/ntfs: Correct possible infinite loops/hangs

fs/ntfs: Correct possible infinite loops/hangs

Correct several infinite loops/hangs found during fuzzing. The issues
fixed here could occur if certain specific malformed NTFS file systems
were presented to GRUB. Currently, GRUB does not allow NTFS file system
access when lockdown mode is enforced, so these should be of minimal
impact.

The changes made in this commit generally correct issues such as attempting
to iterate through a buffer using a length read from the NTFS file system
without confirming the length is larger than 0.

Signed-off-by: Andrew Hamilton <adhamilt@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>