Support unversioned core data models

[freak4pc]

Short description 📝

Reported by @natanrolnik.
I fixed core data versioning in #2612, but forgot to handle the case a core data model has no version at all.

Checklist ✅

• The code architecture and patterns are consistent with the rest of the codebase.
• The changes have been tested following the documented guidelines.
• The CHANGELOG.md has been updated to reflect the changes. In case of a breaking change, it's been flagged as such.
• In case the PR introduces changes that affect users, the documentation has been updated.

[kwridan]

Thanks for adding support for this @freak4pc

[pepicrft]

Besides @kwridan's comment, I'd also update the CHANGELOG.

[natanrolnik]

Thanks for quickly adding this fix, @freak4pc !