Crash when campaign is null

[niklasva82]

When an event is a standalone event, it doesn't show up in the list of events, instead no events show up and an exception is thrown instead.

Steps to reproduce:

1. Create a new event as part of a project.
2. Create a new event as a standalone event.
3. Start calling.

Expected: Both events should show up in the event list.

Actual: No events show up and instead an exception is thrown because campaign is null.