Fix performance problem on Windows

Author: yhirose

httplib.h

@@ -7993,18 +7993,14 @@ inline bool Server::listen_internal() {
     std::unique_ptr<TaskQueue> task_queue(new_task_queue());
 
     while (svr_sock_ != INVALID_SOCKET) {
-#ifndef _WIN32
       if (idle_interval_sec_ > 0 || idle_interval_usec_ > 0) {
-#endif
         auto val = detail::select_read(svr_sock_, idle_interval_sec_,
                                        idle_interval_usec_);
         if (val == 0) { // Timeout
           task_queue->on_idle();
           continue;
         }
-#ifndef _WIN32
       }
-#endif
 
 #if defined _WIN32
       // sockets connected via WASAccept inherit flags NO_HANDLE_INHERIT,