Fixed error when nodeCommands[0] is undefined in Model.updateColor()

[KeyboardSounds]

Fixes #9273
Fixes #8394
Fixes #9278

Model.js was missing code to handle the case in updateColor where nodeCommands.length == 0.

---

Background

For some reason that I ran out of time to diagnose, this PR to TerriaJS is hitting a case where nodeCommands[0] in Model.updateColor() is undefined. This seems like something that shouldn't happen, but this PR stops Cesium from throwing an error and doesn't seem to have any negative consequences.

[cesium-concierge]

Thanks for the pull request @KeyboardSounds!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[lilleyse]

Thanks @KeyboardSounds! Could you also add the same fix to updateBackFaceCulling and updateSilhouette and update CHANGES.md?

[KeyboardSounds]

Done :)

[lilleyse]

Thanks, I'll review soon so we can get this in the next release.

Also CC #9278 - a related bug report that should be fixed by this PR.

[lilleyse]

I'm not able to reproduce the bug even with the multiple issues open #9273 #8394 #9278 which has made it a little hard to debug why it's happening.

updateColor, updateBackFaceCulling, and updateSilhouette should only get called if the model is loaded, meaning its node commands should have already been created. In #8394 @verybigzhouhai mentioned that the glTF had a mesh with no primitives which explains why nodeCommands would be empty, though I don't think this would be a valid glTF. But this doesn't seem to always be the cause because the tileset in #9278 passes the glTF validator (via the 3D Tiles validator), so maybe something else is going on.

Still, it's a good fix and I'm happy with with merging it. Thanks @KeyboardSounds!