PR59612: Print the ap_expr() error message when an expression cannot

be evaluated in forward-dns provider.

Submitted By: Tianyin Xu <tixu cs.ucsd.edu>
Committed By: covener



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1745034 13f79535-47bb-0310-9956-ffa450edef68