HTTP 500 server error with task-configuration-inspector and invalid collection ID

On https://debusine.debian.net/debian/developers/task-configuration-inspector/, you will find links like https://debusine.debian.net/debian/developers/task-configuration-inspector/?collection=433.

But if you replace 433 with some other invalid ID, you will generate a server error triggering a mail to the server admin. We should fail gracefully with an HTTP 404 instead.