fix(charts): prevent displaying stats before requests are made
fix(charts): prevent displaying stats before requests are made

Stat history would be charted by the client as a stream of consciousness
from the runners until they are stopped.
The client will no longer show unquantified stats (represented by the
number of requests).

Issue: #1852

locustio/locust,mbeacom/locust,mbeacom/locust,mbeacom/locust,mbeacom/locust,locustio/locust,locustio/locust,locustio/locust