message: fix a typechecking nit
diff: @@ -28,7 +28,7 @@ export default async function startServer(configDir: ?string): Promise<void> {
  return;
  }
  - if (message.id !== undefined || message.id !== null) {
  + if (message.id != null) {
  processIPCRequestMessage(message, configDir);
  } else {
  processIPCNotificationMessage(message);
  