Should never happen: FOund a history with no enteries

[VladimirAkopyan]

What is it and why is it a problem?

[VladimirAkopyan]

This happens in a block that tries to get find the latest download for a given device. If that device has no data in the latest SensorHistory, we throw a warning. In reality, doing so is totally unnecessary.
Need to just decide what to do in this case. Related to #77

[VladimirAkopyan]

I should edit the method to go back in time until it can find a SensorHistory record for that device. then we query from there, onwards.
That way we have a consistent logic - the app only trusts the datapoints themselves as date-stamps. Nothing else qualifies. If you created 50 days after that - well, what the hell is creating all the data??

[VladimirAkopyan]

#83