Fix a rare memory corruption possibility in mod_dir if the index

file is negotiable and no acceptable variant can be found.
The alternative solutions of using a copy-over version of ap_overlay_tables
worked, but had other drawbacks, so we'll just keep it simple for now.

Submitted by:	Dean Gaudet
Reviewed by:	Roy Fielding, Martin Kraemer


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@82756 13f79535-47bb-0310-9956-ffa450edef68