geom_label: Add more validation for NTFS volume tasting
- Ensure that the computed MFT record size isn't negative or larger than maxphys before trying to read $Volume.
- Guard against truncated records in volume metadata.
- Ensure that the record length is large enough to contain the volume name.
- Verify that the (UTF-16-encoded) volume name's length is a multiple of two.
PR: 258833, 258914
Sponsored by: The FreeBSD Foundation
(cherry picked from commit f0a08fa9f532a58f5d7a4814d6eb7ddd49f368da)