Reimport of a MaterialX file as material instance fails

In Main, the reimport does not generate an error but the material instance is not updated.

Repro steps:

• Import the attached carpaint.mtlx as material
• Import the attached carpaint_instance.mtlx as material instance using the newly imported material Car_Paint as parent
• Modify any input value in the carpaint_instance.mtlx
• Reimport

Actual result:

A error message is logged: '[[...]/carpaint_instance.mtlx : '', Unknown] There was no data to import in the provided source data.'

Expected result: The material instance asset is updated