message: gltfio: Fix "_maskThreshold not found" error.
  MaterialGenerator selects a custom blend mode for transmissive models,
  therefore the AssetLoader should look at the material's blend mode when
  it sets up properties, not the one requested by the glTF file.
  Fixes
diff: @@ -977,7 +977,9 @@ MaterialInstance* FAssetLoader::createMaterialInstance(const cgltf_material* inp
  mResult->mMaterialInstances.push_back(mi);
  - if (inputMat->alpha_mode == cgltf_alpha_mode_mask) {
  + // Check the material blending mode, not the cgltf blending mode, because the provider
  + // might have selected an alternative blend mode (e.g. to support transmission).
  + if (mi->getMaterial()->getBlendingMode() == filament::BlendingMode::MASKED) {
  mi->setMaskThreshold(inputMat->alpha_cutoff);
  }
  