Check also for r->content_encoding (now we should have them all...)

for already compressed content in mod_deflate.

PR: 19913
Submitted by: Tsuyoshi SASAMOTO <nazonazo@super.win.ne.jp>
Reviewed by: Jeff Trawick, Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@99898 13f79535-47bb-0310-9956-ffa450edef68