Fix logging of bytes sent for HEAD requests. %b and %B should

log either - or 0, before this patch, they were both logging
the file size.

PR:	8021
Submitted by:	Taketo Kabe <kabe@sra-tohoku.co.jp>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90870 13f79535-47bb-0310-9956-ffa450edef68