mpm_event: make sure wakeup_listener() does its minimal job.

Even if the listener thread is not created yet (i.e. about to be), we must
still tell it to leave, and terminate the worker queue in any case.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1819848 13f79535-47bb-0310-9956-ffa450edef68