* According to RFC2616 13.2.3 1. negative results of age calculations should

  be replaced by zero.

Reported by: Ryujiro Shibuya <rshibuya gmail.com>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@933886 13f79535-47bb-0310-9956-ffa450edef68