As pointed out in MDLSITE-3067, exceptions are raised if a client attempts to access an RSS feed for a context that no longer exists.

The root cause of this is that /rss/file.php is calling get_context_info_array() which uses MUST_EXIST so throws an exception.

It would be good if this was caught and a 404 response returned.

To replicate:

1. Switch RSS on at server level for forums
2. Create a forum with RSS switched on and follow the RSS link
3. Delete the forum
4. Refresh the RSS link
5. You should see an error