Prevent vbd frontend from oopsing if the underlying device doesn't exist.

Signed-off-by: Horms <horms@verge.net.au>
Signed-off-by: Vincent Hanquez <vincent@xensource.com>

linux-2.6-xen-sparse/drivers/xen/blkfront/blkfront.c

@@ -331,7 +331,12 @@ static void connect(struct blkfront_info *info)
 		return;
 	}
 
-        xlvbd_add(sectors, info->vdevice, binfo, sector_size, info);
+	err = xlvbd_add(sectors, info->vdevice, binfo, sector_size, info);
+	if (err) {
+		xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
+		                 info->xbdev->otherend);
+		return;
+	}
 
 	(void)xenbus_switch_state(info->xbdev, NULL, XenbusStateConnected);