mod_macro: Clear macros before initialization to avoid use-after-free

on startup or restart when the module is linked statically. PR 57525

Submitted by: apache.org tech.futurequest.net
Committed by: Yann Ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1656669 13f79535-47bb-0310-9956-ffa450edef68