Example 400 error

The current requests in `ThngApiExample` cause a "400: Bad request" to be returned from the server.

This is because we're requesting a Tng from `thngReader` by ID, but we're using the newly created local copy to do this — the ID is getting passed as `null` & causing the error.

Updated to use the previously created `List<Thng> results` — this has the ID set correctly, so can retrieve the Thng from the endpoint.