SceneViewer fails to open a GLB file with multiple scenes and multiple animations

### Description

This issue is related to the SceneViewer on Android and not the model-viewer.
The demo contains a GLB file with two scenes "first" and "second" and two animations "move" and "rotate".

#### Steps to reproduce
- Open the demo and try to view "Multi Scene and Multi Animation" in AR on an Android device

#### Expected behavior
- Display the "first" scene of the model and play the "move" animation like the model-viewer does

#### Actual behavior
- The SceneViewer shows the message "Couldn't load object" and exits

#### Additional information
The GLB file is valid through Khronos' [glTF Validator](https://github.khronos.org/glTF-Validator/) tool.

Oddly the glTF spec doesn't have a way to assign an animation to a specific scene. My guess is that the SceneViewer stumbles when trying to load the "rotate" animation and can't find any fitting node in the "first" scene.

The demo contains a second model "Multi Scene and Single Animation" in which the second scene does not contain an animation. This one loads just fine.

#### Live Demo

https://jumbled-sepia-hedgehog.glitch.me/

### Version

- Does not apply

### Browser Affected

- Does not apply

### OS

- Android

### AR

- [ ] WebXR
- [x] SceneViewer
- [ ] QuickLook

If this is not the right place to report SceneViewer related issues I apologize. But it seemed through past issues in this repo that it is the most fitting.