monitor: Make "commit FOO" complain when FOO doesn't exist

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/blockdev.c b/blockdev.c
index d74cd1d..f636bc6 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -493,9 +493,11 @@
         bdrv_commit_all();
     } else {
         bs = bdrv_find(device);
-        if (bs) {
-            bdrv_commit(bs);
+        if (!bs) {
+            qerror_report(QERR_DEVICE_NOT_FOUND, device);
+            return;
         }
+        bdrv_commit(bs);
     }
 }