iostream: resolve reads that may be completed while closing
iostream: resolve reads that may be completed while closing

fixes issue that a read may fail with StreamClosedError
if stream is closed mid-read

tornadoweb/tornado,bdarnell/tornado,allenl203/tornado,tornadoweb/tornado,lilydjwg/tornado,allenl203/tornado,lilydjwg/tornado,dongpinglai/my_tornado,tornadoweb/tornado,mivade/tornado,mivade/tornado,bdarnell/tornado,dongpinglai/my_tornado,mivade/tornado,bdarnell/tornado,dongpinglai/my_tornado,mivade/tornado,allenl203/tornado,lilydjwg/tornado,allenl203/tornado,mivade/tornado,dongpinglai/my_tornado,tornadoweb/tornado,lilydjwg/tornado,allenl203/tornado,dongpinglai/my_tornado,dongpinglai/my_tornado,bdarnell/tornado,bdarnell/tornado