If for some reason we failed to query the mr status, we need to make sure
to provide sufficient information for an ambiguous error (guard error on
sector 0).

Fixes: 0a7a08ad ("IB/iser: Implement check_protection")
Cc: <stable@vger.kernel.org>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>