Shaders linked via primvars removed on AiSceneWrite

[compso]

Describe the bug
When a .usd file is loaded and resaved either via kick or AiSceneWrite directly if a shader is only linked via a custom primvar the the shader is removed from the ArnoldUnassignedShaders prim

To Reproduce
Steps to reproduce the behavior:

1. download the example test_custom_shader.usda.zip
2. run the kick comand: kick -i test_custom_shader.usda -resave test_custom_shader_resaved.usda
3. the resulting usda file removed the ArnoldUnassignedShaders nodegraph

Expected behavior
All shaders in and ArnoldUnassignedShaders Prim should remain on resaving the USD file via AiSceneWrite

Used Software Versions

• Arnold: 7.4.4

Additional context
If I remove the line

string inputs:name = "myRefShader"

The nodegaph remains when re-saving

[autodesk-oss-arnold-bot]

Issue synced internally to ARNOLD-17311