JCBC-368: Avoid potential netty deadlock on failing streaming conn.

Change-Id: Ia3246b960e2e05515c0d54214b1732cbaf570c8b
Reviewed-on: http://review.couchbase.org/29539
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>