Remove panic in write_set_change grpc convertion

[musitdev]

Description

Remove the panic in the WriteSet change conversion for the indexer grpc stream.

Type of Change

• New feature
• Bug fix
• Breaking change
• Performance improvement
• Refactoring
• Dependency update
• Documentation update
• Tests

Which Components or Systems Does This Change Impact?

• Validator Node
• Full Node (API, Indexer, etc.)
• Move/Aptos Virtual Machine
• Aptos Framework
• Aptos CLI/SDK
• Developer Infrastructure
• [] Other (specify)

How Has This Been Tested?

Run the indexer test with movement branch.

Key Areas to Review

Checklist

• I have read and followed the CONTRIBUTING doc
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I identified and added all stakeholders and component owners affected by this change as reviewers
• I tested both happy and unhappy path of the functionality
• I have made corresponding changes to the documentation

[l-monninger]

Good with me by the same token as the other update was good.