Fix Regression: Alerts without fingerprint cannot be moved back to open state

What does this MR do?

In !36527 (merged), we changed from relying on model validations to detecting an error early and raising it to the UI.

This is a lot cleaner, however while doing this we introduced a bug where a non-fingerprinted alert (fingerprint: nil, or fingerprint: ' ' etc..) would always error when transitioning into an open status.

Test scenario:

• Create 2 or more alerts without a fingerprint (To do this, ensure you are on a license < Premium, otherwise Automatic grouping will occur.
• Transition one of them to resolved.
• Try to transition it back to triggered - on master this will fail. On this branch it will succeed.

No changelog needed as this was added + fixed within a release.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #229739 (closed)