fix buglet in previously-committed prctl() feature

before this patch, prctl() would be issued even if CoreDumpDirectory
was not coded...  no big deal, but not intended

now the behavior matches that of httpd 2.*

Submitted by: Jeff Trawick
Reviewed by:  Bill Stoddard, Greg Ames


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@102514 13f79535-47bb-0310-9956-ffa450edef68