HTTPASYNC-77: system resources are not correctly deallocated if I/O reactor is shut down while still inactive (not started)

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1598891 13f79535-47bb-0310-9956-ffa450edef68
HTTPASYNC-77: reverted previous revision; applied a better fix

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1598895 13f79535-47bb-0310-9956-ffa450edef68