Worker::isRunning() returns false after its run() method exits, even if it's running tasks

[dktapps]

An interesting bug recently surfaced in PM: pmmp/PocketMine-MP@61077c4

In my opinion, a worker should always be considered "running" as long as it hasn't shut down, because internally what's essentially happening is this:

while(!$this->shutdown && $this->queue->count() > 0){
    $task = $this->queue->synchronized(function() : void{
        while($this->queue->count() === 0){
            $this->queue->wait();
        }
        return $this->queue->shift();
    });
    $task->run();
}

If a Worker was implemented in userland, this wouldn't be a problem.