Issue title: Wrong placeholder in editor error message for non-existing event
 Issue body: When you try opening the new editor win an identifier from a non-existing event, you get an wrror message like this:
```
Status 404: Event '{123}' not Found
```
The inner `{}` shouldn't be there.
The error message is generated by Opencast's backend.

![Screenshot from 2022-10-13 17-08-28](https://user-images.githubusercontent.com/1008395/195636255-186a1b17-b36b-4715-ac51-1a560773fa88.png)

 Comments: 
 Comment 0: Hello @lkiesow Can you please assign this issue to me. I would like to work on that.
 Comment 1: Go ahead. Thanks for taking this on. If you can, please base your work on the `r/12.x` branch. This can certainly go into the stable branch directly.
 Comment 2: The relevant code for this should be domewhere in here:
- https://github.com/opencast/opencast/tree/b49d0b146791224283a8d16c4976610f25352846/modules/editor-service/src/main/java/org/opencastproject/editor
 Comment 3: Okay @lkiesow Thanks for the above info!

{'source': 'GithubIssues', 'repo_name_with_owner': 'opencast/opencast', 'issue_id': 1407987966, 'repo_stars': 322.0}