BMediaEventLooper: Use enqueue_time in a different shape

* This is the only solution that allowed to use the best
of both ways to do this calculus. I've also tested it
with a modified sound player that snoozed every time
the buffer should be handled, and found that neither
of the lateness calculus I tested (including enqueue_time)
really solve all problems. That's why I've tried to find
an average solution. There's still room for improvements
eventually.

headers/os/media/TimedEventQueue.h

@@ -38,8 +38,9 @@ struct media_timed_event {
 			int32				data;
 			int64				bigdata;
 			char				user_data[64];
+			bigtime_t			enqueue_time;
 
-			uint32				_reserved_media_timed_event_[8];
+			uint32				_reserved_media_timed_event_[6];
 };