  o Minor bugfixes (scheduler, channel):
    - Ignore channels that have been closed while flushing cells. This can
      happen if the write on the connection fails leading to the channel being
      closed while in the scheduler loop. This is not a complete fix, it is a
      bandaid until we are able to refactor those interactions. Fixes bug
      23751; bugfix on 0.3.2.1-alpha.
