Fix a segfault in apr_proc_other_child_unregister. Jeff recently made

Fix a segfault in apr_proc_other_child_unregister. Jeff recently made
a change in APR otherchild.c to unregister all OC registrations as
part of pool cleanup.  This means that we must NOT explicitly call
apr_proc_other_child_unregister out of other pool clean-up routines.
In this case, the OC cleanup was being called first then the piped_log_cleanup
was being called which called apr_proc_other_child_unregister.

We could fix this by detecting the case when there are no more OCs registered
in apr_proc_other_child_unregister but that might just mask other problems we
need to fix anyway.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@89133 13f79535-47bb-0310-9956-ffa450edef68