Stopping a StopWatch that's not started

[ixid]

This may not qualify as a bug though it's not helpful. If you 
stop a StopWatch from std.datetime that's not been started it 
gets set to a garbage time value rather than remaining at 0. This 
seems like inconsistent behaviour as stopping a started stopwatch 
retains the time value that it had when it was stopped. A linked 
enhancement request would be that it would be nice to have a 
dedicated 'isStarted' boolean member function to check if a 
StopWatch is running or not rather than checking that time has 
passed.