mod_proxy_ftp: Fix segfaults on IPv4 requests to hosts with DNS AAAA records.

PR 40841.

trunk patch: http://svn.apache.org/viewvc?rev=1404625&view=rev
             http://svn.apache.org/viewvc?rev=1420223&view=rev
2.4.x patch: http://people.apache.org/~jorton/proxyftpepsv-24.patch
Submitted by: jorton
Reviewed by: jim, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1422578 13f79535-47bb-0310-9956-ffa450edef68