Workaround against commit f500a6d3c2b9ef0bb06d0080d91d8ed3c1d68f58

--- a/block/rbd.c	2013-03-27 02:16:53.000000000 +0300
+++ b/block/rbd.c	2013-03-27 02:17:31.000000000 +0300
@@ -544,6 +544,9 @@ static void qemu_rbd_close(BlockDriverSt
 {
     BDRVRBDState *s = bs->opaque;
 
+    if (!s->image)
+        return;
+
     close(s->fds[0]);
     close(s->fds[1]);
     qemu_aio_set_fd_handler(s->fds[RBD_FD_READ], NULL, NULL, NULL, NULL);
@@ -766,7 +769,7 @@ static int qemu_rbd_co_flush(BlockDriver
 #if LIBRBD_VERSION_CODE >= LIBRBD_VERSION(0, 1, 1)
     /* rbd_flush added in 0.1.1 */
     BDRVRBDState *s = bs->opaque;
-    return rbd_flush(s->image);
+    return s->image ? rbd_flush(s->image) : 0;
 #else
     return 0;
 #endif