[Bug]: Segfault when manifest is empty

[Carmina16]

Checklist

• [X] I agree to follow the Code of Conduct that this project adheres to.
• [X] I have searched the issue tracker for a bug that matches the one I want to file, without success.

flatpak-builder version

1.2.2

Flatpak version

1.10.6

How to reproduce

Call flatpak-builder with an empty file without .yml extension.

Expected Behavior

It says something sensible.

Actual Behavior

It segfaults.

Additional Information

No response