Pipeline display is broken on pull requests from forks

Summary

In the following situation:

• A pull request is sent from a fork of a project.
• The repo has not enabled the build pipeline for forks.

Steps to reproduce

Go to the pull request, you'd see a broken build:

What is the current bug behavior?

clicking on the pipeline icon will result in a 404 page, clicking on the pipeline details will open an empty dropdown and print a red banner on top of the page: "Something went wrong on our side."

What is the expected correct behavior?

It should not show a build, as there is none, as builds are disabled for forks.

Output of checks

This bug happens on GitLab.com. E.g. here: https://gitlab.com/uTox/uTox/merge_requests/790/diffs