name-based vhosts listed twice with apachectl -S

When processing a vhost with * or _default_, we'd add the "names" once
for 0.0.0.0 and once for [::], but these are stored in the same "default"
ip chain.  Catch the back-to-back wildcard + same port and short-circuit the
second add.

Submitted By: rjung
Committed By: covener


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1525000 13f79535-47bb-0310-9956-ffa450edef68