event: Fix worker-listener deadlock in graceful restart caused by get_worker()

allocating new worker after ap_queue_info_term(), but not setting the
have_idle_worker variable. PR 56960.

Submitted By: Zin UDA
Committed By: jkaluza


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1629577 13f79535-47bb-0310-9956-ffa450edef68