Render delegate crashes when changing a variant of a shader

[sirpalee]

Describe the bug Changing a variant on a shader causes the render delegate to crash.

To Reproduce Steps to reproduce the behavior:

1. Open the attached arnold_vari_hang.usda.zip file in usdview and switch to Arnold.
2. Change the color variant on /root/looks/material/shader from blue to red.

Used Software Versions

• Arnold: 6.2.0.1
• USD: 21.02
• Compiler: GCC 6.3.1
• OS: CentOS 7

[sirpalee]

This is very likely because of PixarAnimationStudios/USD#978 .

When the variant is on the shader, changing the variant will destroy the existing material hydra primitive, but Hydra won't create a new one and assign it to the shader. If the variant is on the material, everything works as expected.

[sirpalee]

I'm moving this back to ticket triage, as we are depending on an upstream fix.

[autodesk-oss-arnold-bot[bot]]

Issue synced internally to ARNOLD-13268