Blender: Workfile instance update fix

[iLLiCiTiT]

Changelog Description

Make sure workfile instance has always available 'instance_node' in transient data.

Additional info

The instance node was available only if something had changed or the instance was created.

Testing notes:

1. Launch blender
2. Open publisher tool
3. Save and Reset tool
4. There should not be any issue saving it

[moonyuet]

I have tested with Blender.
Save and reset works as expected. But I do have a question: Is it normal for the optional extractor always turned off after save while I turned on it (before save)?
You can find the video below as reference.
https://github.com/ynput/OpenPype/assets/64118225/2ba0e727-aff6-4b2f-a46c-c3e1d292afb0

[BigRoy]

I have tested with Blender. Save and reset works as expected. But I do have a question: Is it normal for the optional extractor always turned off after save while I turned on it (before save)? You can find the video below as reference. https://github.com/ynput/OpenPype/assets/64118225/2ba0e727-aff6-4b2f-a46c-c3e1d292afb0

No, that would be a bug. The value should persist.

However since that toggle is not on the workfile instance I believe it has nothing to do with this PR and likely was a bug prior to it?