* util/biosdisk.c (get_drive): Verify that `map[i].drive' is non-NULL
before dereferencing it.
* fs/fat.c (struct grub_fat_bpb): Move fat32-specific fields into a
union with fat12/fat16-specific ones. Add some new fields, including
`num_serial' for both versions.
(struct grub_fat_data): Add `uuid' member.
(grub_fat_mount): Refer to fat32-specific fields in `bpb' by their new
names. Initialize `data->uuid' using `num_serial'.
(grub_fat_uuid): New function.
(grub_fat_fs): Reference grub_fat_uuid() in `uuid' struct member.
* fs/reiserfs.c (grub_reiserfs_superblock): Add `uuid' field.
(grub_reiserfs_uuid): New function.
(grub_reiserfs_fs): Reference grub_reiserfs_uuid() in `uuid' struct
member.
* fs/xfs.c (grub_xfs_sblock): Add `uuid' field.
(grub_xfs_uuid): New function.
(grub_xfs_fs): Reference grub_reiserfs_uuid() in `uuid' struct member.