Fix number of bytes copied by read_connection() in src/support/ab.c

Submitted by: Jim Cox <jc@superlink.net>
Reviewed by: Ralf S. Engelschall
PR: 4271


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@83109 13f79535-47bb-0310-9956-ffa450edef68