python: let libvirt_virConnectDomainEventCallback indicate success

* python/libvir.c (libvirt_virConnectDomainEventCallback): Return 0
when successful, rather than always returning -1.
clang flagged this function for its dead-store of "ret=0".
Once "ret" was set to 0, it was never used, and
the function would always return -1.

python/libvir.c

@@ -4,7 +4,7 @@
  *           entry points where an automatically generated stub is
  *           unpractical
  *
- * Copyright (C) 2005, 2007, 2008 Red Hat, Inc.
+ * Copyright (C) 2005, 2007-2009 Red Hat, Inc.
  *
  * Daniel Veillard <veillard@redhat.com>
  */
@@ -1812,7 +1812,7 @@ libvirt_virConnectDomainEventCallback(virConnectPtr conn ATTRIBUTE_UNUSED,
 
 cleanup:
     LIBVIRT_RELEASE_THREAD_STATE;
-    return -1;
+    return ret;
 }
 
 static PyObject *