### Godot version

v4.0.beta16.official [518b9e580]

### System information

Windows 10

### Issue description

`RichTextLabel` with `threaded` enabled may crash the game or show the following warning if the node is in another scene:

```
W 0:00:03:0802   test.gd:12 @ load_with_scene(): A Thread object has been re-started without wait_to_finish() having been called on it. Please do so to ensure correct cleanup of the thread.
  <C++ Source>   core/os/thread.cpp:76 @ start()
  <Stack Trace>  test.gd:12 @ load_with_scene()
                 test.gd:6 @ load_items()
                 test.gd:26 @ _on_button_pressed()
```

It may crash the game (without any warning) if it's added directly.

In `v4.0.beta15.official [4fa6edc88]` I was able to reproduce the same warning on my project but I can't reproduce it in the attached MRP. I get a different error and will crash too if the node is added directly:

```
E 0:00:03:0019   remove_from_group: Condition "!E" is true.
  <C++ Source>   scene/main/scene_tree.cpp:157 @ remove_from_group()
```


### Steps to reproduce

Click on the  `Load with scene` or `Load with node` buttons in the attached MRP until it shows a warning/error or crashes. It may take a while.

### Minimal reproduction project

[add_chid_bug_b16.zip](https://github.com/godotengine/godot/files/10521402/add_chid_bug_b16.zip)

for (int j = 0; j <= i; j++) {
				total_height = _resize_line(main, j, theme_cache.normal_font, theme_cache.normal_font_size, text_rect.get_size().width - scroll_w, total_height);
				main->first_invalid_line.store(j);
				main->first_resized_line.store(j);
				main->first_invalid_font_line.store(j);
			}
		}
		vscroll->set_max(total_height);
		vscroll->set_page(text_rect.size.height);
		if (scroll_follow && scroll_following) {
			vscroll->set_value(total_height);
		}
		updating_scroll = false;
		main->first_invalid_line.store(i);
		main->first_resized_line.store(i);
		main->first_invalid_font_line.store(i);
		if (stop_thread.load()) {
			return;
		}
		loaded.store(double(i) / double(main->lines.size()));
	}
	main->first_invalid_line.store(main->lines.size());
	main->first_resized_line.store(main->lines.size());
	main->first_invalid_font_line.store(main->lines.size());
	if (fit_content) {
		update_minimum_size();
	}
	emit_signal(SNAME("finished"));
}
void RichTextLabel::_invalidate_current_line(ItemFrame *p_frame) {