* modules/proxy/config.m4: Avoid sh syntax error with

  autoconf 2.63, where an empty "else" clause gets 
  generated from the args if present with only whitespace.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1157094 13f79535-47bb-0310-9956-ffa450edef68