document swfdec_buffer_queue_peek
document swfdec_buffer_queue_peek

I wasn't sure if I need to unref the buffer. So better to check it only once
and then documenting instaed of having to do it again ;)

freedesktop-unofficial-mirror/swfdec__swfdec,mltframework/swfdec,freedesktop-unofficial-mirror/swfdec__swfdec,freedesktop-unofficial-mirror/swfdec__swfdec,mltframework/swfdec