event MPM: Provide error handling for ThreadStackSize. PR 54311

trunk patch: http://svn.apache.org/r1433682
Submitted by: Tianyin Xu <tixu cs.ucsd.edu>
Reviewed by: minfrin, jailletc36, sf


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1481515 13f79535-47bb-0310-9956-ffa450edef68