EventLagMonitor's interval function doesn't stop with Pace.stop

[barkofdelight]

EventLagMonitor creates an interval function with setInterval, but this repeating function only is stopped when the computed lag has fallen sufficiently.

If the progress bar is stopped and restarted, the repeating function might be left running, so there will now be two such functions.

Although this might not seem like a problem because the two functions would be evaluating the same thing, it's not expected behavior.