BUG/MEDIUM: logs: fix http-client's log srv initialization

As anticipated in commit 211ea252d ("BUG/MINOR: logs: fix logsrv leaks
on clean exit"), there were indeed other corner cases that were not
properly covered. Setting the http client's ring_name to NULL make the
sink lookup crash on startup in sink_find () with a config as simple as:

    global
        log ring@buf0 local0

The fields must be properly initialized (both config file name and
the ring_name). This only needs to be backported if/when the commit
above is backported.
diff --git a/src/http_client.c b/src/http_client.c
index f1e5345..6bf28d0 100644
--- a/src/http_client.c
+++ b/src/http_client.c
@@ -1089,9 +1089,8 @@
 		memcpy(node, logsrv, sizeof(*node));
 		LIST_INIT(&node->list);
 		LIST_APPEND(&curproxy->logsrvs, &node->list);
-		node->ring_name = NULL;
-		node->conf.file = NULL;
-		node->conf.line = 0;
+		node->ring_name = logsrv->ring_name ? strdup(logsrv->ring_name) : NULL;
+		node->conf.file = logsrv->conf.file ? strdup(logsrv->conf.file) : NULL;
 	}
 	if (curproxy->conf.logformat_string) {
 		curproxy->conf.args.ctx = ARGC_LOG;