Add failure message for self-subscribing users for whom court data could not be found

[brittberwanger]

For users who attempt to self-subscribe, if we find no events within the time to live timeframe, make sure to send them a message explaining this and allow them to resubscribe.

This needs to be sure to not send messages over correct conditions where there are no more upcoming events, such as closed cases.

[brittberwanger]

It looks like the service already does this, it would not hurt to review that code before closing this out.