fix segfault which occured if the filename was not

set, for example, when processing some error conditions.

PR: 23836
Reviewed by: Jeff Trawick, Cliff Woolley


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@101539 13f79535-47bb-0310-9956-ffa450edef68