add empty string handler

[magdaaniol]

Currently the reset_stream event handler is not catching any exceptions. We should minimally handle the empty stream exception and malformed task structure exception.

This PR added the handler of empty stream (which is likely to happen because the query might not return any results).
The malformed task structure is less likely and it is now failing with console error (before it was hanging in an infinite loop) It's hard to catch without modifying the current front end. Ideally, we would be validating the stream before sending it to the front end, but for that we need structured stream planned for Prodigy v2.

[koaning]

It seems I still get notifications. That said, I figured I might share this blogpost with a cautionary tale about lunr. Lessons learned over at calmcode.

https://calmcode.io/blog/memory

[magdaaniol]

Thanks @koaning

It seems I still get notifications.

I suppose it's because you're watching this repo? :)