http_filters: Don't send 100-continue when 4xx is due

PR 43711
Reported & tested by Ragini Bisraya
Patch by Chetan Reddy
Reviewed: niq


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@628644 13f79535-47bb-0310-9956-ffa450edef68