Immediately close channel when subscribers cancel (AsyncHttpClient#1459)

This commit includes two changes: - More aggressively mark the ResponseFuture as done to avoid threading issues that still read the old state - Directly invoke channel closing, since there is no guarantee of another channelRead occuring (e.g. if the stream was hard closed)

Author: HKrausAxon

client/src/main/java/org/asynchttpclient/netty/handler/StreamedResponsePublisher.java

@@ -42,16 +42,15 @@ public StreamedResponsePublisher(EventExecutor executor, ChannelManager channelM
  protected void cancelled() {
  logger.debug("Subscriber cancelled, ignoring the rest of the body");
 
- // The subscriber cancelled early, we need to drain the remaining elements from the stream
- channelManager.drainChannelAndOffer(channel, future);
- channel.pipeline().remove(StreamedResponsePublisher.class);
-
  try {
  future.done();
  } catch (Exception t) {
  // Never propagate exception once we know we are done.
  logger.debug(t.getMessage(), t);
  }
+
+ // The subscriber cancelled early - this channel is dead and should be closed.
+ channelManager.closeChannel(channel);
  }
 
  NettyResponseFuture<?> future() {