problem with touch cache file

Hi, i found en fix another bug...

You always are touching cache file and it get a warning on my host... so i put a check if file exists...

...

/**
 * sets the chat's cache file by touching it
 */
function chatroom_chat_set_cache($chat_id) {
  $chat_file = chatroom_chat_get_cache_file_path($chat_id);
  if (file_exists($chat_file)) {
    return;
  }
  @touch($chat_file);
}

...