wavparse: When flushing on EOS, don't process more data than the "data" size
Even if we have more data queued up when flushing than the size of the data chunk, don't process and output it. If the data size is known, this likely contains another chunk (e.g. an INFO chunk) or things like ID3 tags. Just outputting them as if they were data is going to cause unexpected behaviour and unpleasant audio noises.