WebIDE doesn't work on empty repositories

Summary

If you open a project with an empty repository in the Web IDE directly via the URL, errors are shown.

Steps to reproduce

1. Create a new empty project. Do not create the project with a README
2. Open the project via direct url: https://gitlab.com/-/ide/project/<group>/<project>/edit/master/-/

What is the current bug behavior?

Errors are shown and the IDE is unusable.

What is the expected correct behavior?

Web IDE should be usable and have a nice empty state

Note that this Issue is about empty-repositories only. For non-existent branches in a non-empty repositories, we still should show an error with the button to create a branch.

Relevant logs and/or screenshots

Output of checks

This bug happens on Gitlab.com