Fix "TypeError: pages[offset] is undefined"

[Arnei]

This patch fixes the above error from the webconsole.

How to test this

The error message in the web console can only consistently be seen when running the admin locally via npm start, so I suggest doing that. Functionality should otherwise remain unchanged, so test that all pages load as usual.

[github-actions]

This pull request is deployed at test.admin-interface.opencast.org/1022/2024-12-19_14-49-41/ .
It might take a few minutes for it to become available.

[github-actions]

Use docker or podman to test this pull request locally.

Run test server using develop.opencast.org as backend:

podman run --rm -it -p 127.0.0.1:3000:3000 ghcr.io/opencast/opencast-admin-interface:pr-1022

Specify a different backend like stable.opencast.org:

podman run --rm -it -p 127.0.0.1:3000:3000 -e PROXY_TARGET=https://stable.opencast.org ghcr.io/opencast/opencast-admin-interface:pr-1022

It may take a few seconds for the interface to spin up.
It will then be available at http://127.0.0.1:3000.
For more options you can pass on to the proxy, take a look at the README.md.