Denotes that the isolate died due to an exception.
This event is sent after ReactorStarted.
This event is sent before ReactorTerminated, *unless* the exception is thrown
while ReactorTerminated is being processed, in which case the ReactorDied is
Note that, if the exception is thrown during the isolate constructor invocation
and before the appropriate event handler is created, this event cannot be sent
to that event handler.
the exception that the isolate threw