according to the documents, http://www.tornadoweb.org/en/stable/_modules/tornado/iostream.html#BaseIOStream.read_until_close
if streaming_callback is given, the argument to final callback is empty
but seems not always the case
test code is here : https://gist.github.com/wynemo/5488772
it shows sometimes streaming_callback is given, but not be called, and the final callback's argument is not empty.
Fix another case in which streaming read_until_close passed data to t…
…he final callback.
Oops, I fixed a similar issue in 3.0 but looks like there was another case I missed.