HTTPASYNC-51: Request producers do not get correctly reset if the server responds early (out of sequence), which can cause entity enclosing requests to be malformed in case of re-execution

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1511206 13f79535-47bb-0310-9956-ffa450edef68