Possible race condition: trying to add count

[mrfuxi]

Occasional when closing down data channel after time is up, we are still trying to push new data to it because it happens it's also the time to update client with new counts.

We one of:

• synchronization (might be overkill)
• don't send data if there is nothing to send (might do the trick as a that point there should be no more new data)
• check is channel open (how?)

Error: panic: send on closed channel