bgpd: bgp_scan shouldn't queue up route_nodes with no routes for processing

* bgp_nexthop.c: (bgp_scan) There is little point queueing an rn with no routing
  information for processing.
* bgp_route.c: (bgp_process) Do nothing on rn's with no routes. Add an assert
  for now, to try catch any other cases, but prob should be removed.
  (bgp_best_selection) rn with no routes == finish early.
diff --git a/bgpd/bgp_nexthop.c b/bgpd/bgp_nexthop.c
index 145a1d8..607d99b 100644
--- a/bgpd/bgp_nexthop.c
+++ b/bgpd/bgp_nexthop.c
@@ -496,7 +496,8 @@
 					   afi, SAFI_UNICAST);
 	    }
 	}
-      bgp_process (bgp, rn, afi, SAFI_UNICAST);
+      if (rn->info)
+        bgp_process (bgp, rn, afi, SAFI_UNICAST);
     }
 
   /* Flash old cache. */