control EXTENDCIRCUIT: check node_has_preferred_descriptor().

Suggested by teor during code review for 25691.

src/or/control.c

@@ -3492,17 +3492,19 @@ handle_control_extendcircuit(control_connection_t *conn, uint32_t len,
   smartlist_free(args);
 
   nodes = smartlist_new();
+  int first_node = zero_circ;
   SMARTLIST_FOREACH_BEGIN(router_nicknames, const char *, n) {
     const node_t *node = node_get_by_nickname(n, 0);
     if (!node) {
       connection_printf_to_buf(conn, "552 No such router \"%s\"\r\n", n);
       goto done;
     }
-    if (!node_has_any_descriptor(node)) {
+    if (!node_has_preferred_descriptor(node, first_node)) {
       connection_printf_to_buf(conn, "552 No descriptor for \"%s\"\r\n", n);
       goto done;
     }
     smartlist_add(nodes, (void*)node);
+    first_node = 0;
   } SMARTLIST_FOREACH_END(n);
   if (!smartlist_len(nodes)) {
     connection_write_str_to_buf("512 No router names provided\r\n", conn);
@@ -3515,14 +3517,15 @@ handle_control_extendcircuit(control_connection_t *conn, uint32_t len,
   }
 
   /* now circ refers to something that is ready to be extended */
-  int first_node = zero_circ;
+  first_node = zero_circ;
   SMARTLIST_FOREACH(nodes, const node_t *, node,
   {
     extend_info_t *info = extend_info_from_node(node, first_node);
     if (!info) {
       tor_assert_nonfatal(first_node);
       log_warn(LD_CONTROL,
-               "controller tried to connect to a node that doesn't have any "
+               "controller tried to connect to a node that lacks a suitable "
+               "descriptor, or which doesn't have any "
                "addresses that are allowed by the firewall configuration; "
                "circuit marked for closing.");
       circuit_mark_for_close(TO_CIRCUIT(circ), -END_CIRC_REASON_CONNECTFAILED);