NULLing eventsRunLoop may crash later

Because the STKAudioPlayer calls:

                [currentlyReadingEntry.dataSource unregisterForEvents];
                [currentlyReadingEntry.dataSource close];

Or when calling [close] and then [open] immediately

**Something happened to the previous PR https://github.com/tumtumtum/StreamingKit/pull/149 so this is a retry**