NetworkError when copying a Sketchfab model URL from the room to use as a spawner element prevents scene publishing

[misslivirose]

Issue: The following error message appears when you have spawner objects in a room that references an object URL that was added and copied from the scene.

Repro Steps:

1. In Spoke, add an object from Sketchfab [Object A] into your scene. I have reproduced this with 3 models (and stopped testing after that)
2. Add the spawner object into the scene [Object B]
   2.5 (Optional verification step - observe that you are able to publish with the default spawner model of the Hubs Duck)
3. Select Object A and copy the URL from the properties
4. Select Object B and paste the URL into the spawner properties
5. Observe that all objects display correctly
6. Publish your scene
7. Observe that you get the error above

Impact
Most users would likely not be able to work around this. I have not yet figured out how to work around other than deleting the objects. To figure out which objects were causing the issue, I had to export the original scene throwing the NetworkError at publish time as a legacy Spoke file, then reimport it in a new project to find the errors at import time.

Console Error

Security Error: Content at https://hubs.mozilla.com/spoke/projects/Hc3tSTp may not load data from blob:https://hubs.mozilla.com/711fd441-157c-42d8-84bb-120fbece04af.
Security Error: Content at https://hubs.mozilla.com/spoke/projects/Hc3tSTp may not load data from blob:https://hubs.mozilla.com/833731c2-b1a3-4479-b72e-77ec4392489f.
o: Error exporting scene:
  Cause:
    NetworkError when attempting to fetch resource.
    r errors.js:29
    o errors.js:37
    exportScene Editor.js:404
    publishProject Api.js:786
    Vp EditorContainer.js:841
    React 9
    unstable_runWithPriority scheduler.production.min.js:20
    React 3
    r helpers.js:59
    _wrapEventTarget trycatch.js:58
    React 8
    unstable_runWithPriority scheduler.production.min.js:20
    React 2
    D scheduler.production.min.js:16
    U scheduler.production.min.js:18
    S scheduler.production.min.js:13
    EventHandlerNonNull* scheduler.production.min.js:14
    Webpack 68

Environment
Firefox desktop (80.0.1)
Windows 10 PC

Tested Model URLs
All models are marked downloadable
https://sketchfab.com/3d-models/shovel-cd26a349f2f6441a8fd1ce5be8c93b6e
https://sketchfab.com/3d-models/pumpkin-509e960db3b3443382b0a189f5abfae0
https://sketchfab.com/models/0a679ef337a04dee98ec55a49bb9d1c7