Treat zero layer dataset as unusable

[youri-k]

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

Steps to test:

• upload a zero layer dataset
• should be marked as unusable in the frontend, but not throw an error

Issues:

• fixes consider zero-layer datasets as inactive #4941

---

• Updated (unreleased) changelog
• [ ] Updated (unreleased) migration guide if applicable
• [ ] Updated documentation if applicable
• [ ] Adapted wk-connect if datastore API changes
• Needs datastore update after deployment
• Ready for review

[fm3]

LGTM, I also tried it and seems to work as expected :)

Does this interact with #4944 ? Will the scale still be available there for zero-layer datasets?

[youri-k]

Yes, this does interact with #4944 and I will make the necessary changes there to make the scale still available.