code: def go_next_thumbnail(self):
          
          if self.current_thumbnail is not None:
              index = self._thumbnails.index(self.current_thumbnail) + 1
              index = 0 if index >= len(self._thumbnails) else index
              self.set_current_index(index)
              self.scroll_to_item(index)
docs: Select thumbnail next to the currently selected one.