Incorrect normals in KHR_materials_unlit tilesets

[kring]

This is Google Photorealistic 3D Tiles, in the 12_CesiumGoogleMapsTiles level of CesiumForUnrealSamples. Note the dark bands:

It's caused by a very incorrect normal:

Checking "Ignore KHR_materials_unlit" on the tileset makes the problem go away:

I noticed this during release testing of v2.9.0, but I'm not sure if it's a new problem in this release. I'll update the issue once I know the answer to that question.

[kring]

This problem first shows up in v2.7.1. It worked fine in v2.7.0.