Take advantage of the new pre_config return value when apr_proc_detach

fails. I'll be making some changes to apr_proc_detach, and it will be
nice to be able to report runtime errors.

Tested on worker but the code changes are identical on other MPMs.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93069 13f79535-47bb-0310-9956-ffa450edef68