btrfs: don't accept bare namespace as a valid xattr
btrfs: don't accept bare namespace as a valid xattr

Due to insufficient check in btrfs_is_valid_xattr, this unexpectedly
works:

 $ touch file
 $ setfattr -n user. -v 1 file
 $ getfattr -d file
user.="1"

ie. the missing attribute name after the namespace.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=94291
Reported-by: William Douglas <07dd1d6cf12120bb0585d2eb50da402be35d56e5@intel.com>
CC: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org> # 2.6.29+
Signed-off-by: David Sterba <a2ce9d316ca04d17b520237d2846a218b8284e52@suse.cz>
Signed-off-by: Chris Mason <e2e8c5702d8ed5f565988a1cf5bb35c9ce199e5e@fb.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs