Fix model crash by adding default pbr material

[lilleyse]

Fixes #6891

Like #6857 (comment), this fix is temporary until #6805 is in.

[cesium-concierge]

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[hpinkos]

@lilleyse do you think #6805 will make it in this release? I don't think we should merge this workaround if we're going to have the actual solution ready to go shortly

[lilleyse]

Fine by me, #6805 should made the release.

[lilleyse]

It's looking like #6805 won't make the release so I reopened this PR.

[hpinkos]

I'm still not convinced we should rush to get this workaround in for the release since we have the actual fix coming soon. Was this issue a common problem that a number of our users are experiencing?

[lilleyse]

It has been brought up twice

• An error occurred while rendering. Rendering has stopped #6940
• Cesium no longer adds a default material for gltf 2.0 as needed #6891

[hpinkos]

Okay, that's significant

[hpinkos]

Who should review this? @likangning93?

[lilleyse]

I think @ggetz has more familiarity with the gltf-pipeline code and would be better to review this.

[ggetz]

Since Source/ThirdParty/GltfPipeline/addDefaults.js will be overridden by the rebuilt GltfPipeline files, I think this fix will be fine temporarily.

[ggetz]

Code looks good and the model from #6891 loads correctly. Thanks @lilleyse !

[hpinkos]

@lilleyse open an issue or add a comment to #6805 to revert this workaround when the actual fix comes in.

[ggetz]

#6805 completely rebuilds the files in GltfPipeline from the new master (as opposed to a previous branch just fro cesium) so this fix will already be overridden.