Fix null pointer exception for loading template request/view.html

There was no check for the reason in a request event to be null in the template.

Additionally, the template expected the reason of any previous request to always be non-null. However, the reason is null for a still processing request. Again, the assumption is that there should be no previous requests that are still being processed. However, automagically closing a lab does this.

The fix adds a null-check in the template and changes the selector for 'previous' requests to filter on whether the previous requests are archived.