Load cesium ion tileset right when available

[jailln]

Load cesium ion tilesets directly after getting the url from the api instead of waiting for the next animation frame.

This is particularly useful in cases where render is triggered asynchronously (and not at each frame) in which case we ask for TilesRenderer update at init and then when load-tile-set and load-model are triggered.

[gkjohnson]

Is there a reason you can't just call update immediately after instantiating the tiles renderer?

tiles = new CesiumIonTilesRenderer( ... );
tiles.update();

[jailln]

It's already what I'm doing but then I'm expecting for the tileset to load and wait for load-tile-set event to execute another tiles.update(). However load-tile-set is never raised since tiles.update() triggers the first call to the cesium ion API which gets resolved with the tileset url but doesn't load the tileset until there is a new tiles.update().

I figured that would make sense that the first call to tiles.update() loads the tileset like for other TilesRenderer.

[gkjohnson]

Oh I see, now - thank you. I think this a fine change to make. Do you mind adding a comment describing why we need to call "update" again here?

[jailln]

Yes of course, it's done

[gkjohnson]

Great, thank you!