Fix translation error in Polish 404 error message.

Submitted by: Mikolaj Menke <miki menek one pl>
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=570228


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@912213 13f79535-47bb-0310-9956-ffa450edef68