Previous attempt was the onCompleted block. However it turns out that
at that point the model still has the old byte amounts.  The order is
showSpeedChanged -> setRefreshRate -> Timer.onCompleted/runningChanged -> model updates
So set the amount to 0 in onCompleted and trigger the Timer on start
(like a Timer with 0 interval). This initial trigger happens after the
 odel gets a new value and we have a correct amount on the first regular
trigger of the Timer.
BUG:420365
FIXED-IN:5.22


(cherry picked from commit d5df9379)