Couldn't upload draco or ktx2 glb as a custom avatar. #6209

Description

GLB files using Draco or KTX2 could not be uploaded as custom avatars.

To Reproduce
Steps to reproduce the behavior:

1. Go to a room
2. Click on 'Join room'
3. Click on 'Change Avatar'
4. Click on 'Create Avatar'
5. Click on 'Custom GLB'
6. Select draco/ktx2 GLB file
7. Click on 'Save'

Expected behavior

Uploading can be done without any errors.

Screenshots

Hardware

• Device: Desktop
• OS: Linux (Arch)
• Browser: Firefox

Additional context

This problem is probably caused by the Loader not being set in the following code.

https://github.com/mozilla/hubs/blob/master/src/react-components/avatar-editor.js#L153-L169