Ensure that ALL fields of the ap_listen_rec structure are initialized

alloc_listener initializes more fields in the created ap_listen_rec structure
than alloc_systemd_listener as it has more data to add to this structure.
Ensure that all fields of the ap_listen_rec structure are initialized at
least with 0 as later code using this structure depends on this.

Submitted by: jailletc36

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1926091 13f79535-47bb-0310-9956-ffa450edef68
(cherry picked from commit 32ebb6b)

Author: rpluem

server/listen.c

@@ -313,9 +313,7 @@ static apr_status_t alloc_systemd_listener(process_rec * process,
     si.type = SOCK_STREAM;
     si.protocol = APR_PROTO_TCP;
 
-    rec = apr_palloc(process->pool, sizeof(ap_listen_rec));
-    rec->active = 0;
-    rec->next = 0;
+    rec = apr_pcalloc(process->pool, sizeof(ap_listen_rec));
 
 
     rv = apr_os_sock_make(&rec->sd, &si, process->pool);