[BUG] http: use correct ACL pointer when evaluating authentication

req_acl was used instead of req_acl_final. As a matter of luck, both
happen to be the same at this point, but this is not granted in the
future.

This fix should be backported to 1.4.
diff --git a/src/proto_http.c b/src/proto_http.c
index 3a404e6..61ec462 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -3148,7 +3148,7 @@
 
 	if (req_acl_final && req_acl_final->action == PR_REQ_ACL_ACT_HTTP_AUTH) {
 		struct chunk msg;
-		char *realm = req_acl->http_auth.realm;
+		char *realm = req_acl_final->http_auth.realm;
 
 		if (!realm)
 			realm = do_stats?STATS_DEFAULT_REALM:px->id;