fat: detect media without partition table correctly

I received a complaint that some FAT formated medias (e.g.  sd memory cards)
trigger a "unknown partition table" message even though there is no partition
table and they work correctly, while in general (when e.g.  formated with
mkdosfs or even Windows Vista) this message is not shown.

Currently this seems only to happen when the medias get formatted with Windows
XP (and possibly Win 2000).  Then the boot indicator byte contains garbage
(part of text message) and so do the other parts checked by msdos_paritition
which then later triggers this message.

References: novell bug #364365

Most fat formatted media without partition table contains zeros in the boot
indication and the other tested bytes and so falls through the checks in
msdos_partition, leading it to return with 1 (all is fine).

But some (e.g.  WinXP formatted) fat fomated medias don't use boot_ind and so
the check fails and causes a "unkown partition table" warning eventhough there
is none and everything would be fine.

This additional check directly verifies if there is a fat formatted medium
without a partition table.

Signed-off-by: Frank Seidel <fseidel@suse.de>
Cc: Andreas Dilger <adilger@sun.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>