render: Don't return blank addresses for pods

A small performance improvement - instead of creating an entry in a
map which doesn't match anything, just skip a pod with a blank IP.

render/pod.go

@@ -116,7 +116,7 @@ func MapPod2IP(m report.Node) []string {
 	}
 
 	ip, ok := m.Latest.Lookup(kubernetes.IP)
-	if !ok {
+	if !ok || ip == "" {
 		return nil
 	}
 	return []string{report.MakeScopedEndpointNodeID("", ip, "")}