Change core_input_filter() so that it returns an empty brigade upon

FIN/EOF or error.  This meshes with what getline() looks for.  It isn't
perfect, but it avoids some nasty loops consuming all available storage
on http/1.1 connections.  In keepalive state, we call getline to read the
next request...  getline() calls core_input_filter() (indirectly)...
core_input_filter() calls apr_recv() which returns APR_SUCCESS/0 bytes
to signal FIN/EOF.  But core_input_filter() returned a bucket with length
zero to getline(), so getline() called core_input_filter() again.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86379 13f79535-47bb-0310-9956-ffa450edef68