Improve the way the chunking filter handles zero-length buckets,

and fix the comment explaining how to reduce the incidence of tiny chunks.
Submitted by:	Jeff Trawick
Reviewed by:	Tony Finch


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86222 13f79535-47bb-0310-9956-ffa450edef68