CalDav dialog never reports no items found

[danirabbit]

What Happened

If we successfully connect to the sever, but find nothing, the state isn't reported properly in the dialog:

Expected Behavior

The save button should remain insensitive and there should be a message explaining that nothing was found

Steps to Reproduce

1. Add a carddav server instead of caldav. Since we're only checking for calendars and tasks, it will connect succesfully but return nothing
2. See that the save button becomes sensitive, but the view still says it's checking