Fix crash in balancer-manager.

This was due to an incomplete refactoring in
r771940 (switching balancer->workers to an
array of pointers).

It's likely that other balancer functionality
was broken too.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@891230 13f79535-47bb-0310-9956-ffa450edef68