Fix segfault when ospf6_create() is not called yet.
Thanks to Mohit Thakur.
diff --git a/ospf6d/ospf6_zebra.c b/ospf6d/ospf6_zebra.c
index bdd3bab..bc15dff 100644
--- a/ospf6d/ospf6_zebra.c
+++ b/ospf6d/ospf6_zebra.c
@@ -57,6 +57,9 @@
   zebra_router_id_update_read(zclient->ibuf,&router_id);
   router_id_zebra = router_id.u.prefix4;
 
+  if (o == NULL)
+    return 0;
+
   if (o->router_id  == 0)
     o->router_id = (u_int32_t) router_id_zebra.s_addr;