On failure to create extend info for an introduction point, don't leak.

This is CID 1438152.  No backport needed: this path is already
inside a BUG() guard.

src/feature/rend/rendservice.c

@@ -4227,6 +4227,7 @@ rend_consider_services_intro_points(time_t now)
        * directly ourselves. */
       intro->extend_info = extend_info_from_node(node, 0);
       if (BUG(intro->extend_info == NULL)) {
+        tor_free(intro);
         break;
       }
       intro->intro_key = crypto_pk_new();