Always clear the C-L if we are going to try to parse the file. It is

Always clear the C-L if we are going to try to parse the file.  It is
impossible for us to determine if there is going to be an SSI tag in the
file until we have actually scanned it all.  By that time, it is likely
that the first chunk of data, and the headers have been sent to the client,
and it is too late to clear the C-L.  If we are parsing the file, we have
to just assume we are going to change the content.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88477 13f79535-47bb-0310-9956-ffa450edef68