PBRCustomMaterial support in GLTF loader

[Evgeni_Popov]

clone is not implemented on CustomMaterial / PBRCustomMaterial, see:

CustomMaterial.clone() Not Currently Working

Hey crew, It looks like CustomMaterial is probably inheriting StandardMaterial’s clone() function, which doesn’t include its custom shader bits and bobs. Here’s a demo: https://www.babylonjs-playground.com/#UXCB15#115 Cheers, Matt

There’s a workaround in a PG linked by @nasimiasl in this thread.

Also, there’s is an error in your PG, m.material can be null, so you should test for it.