### 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)

Size2 ctrl_size = get_size();
	
	for (int line = 0; line < l.text_buf->get_line_count(); line++) {
		if (line > 0) {
			off.y += theme_cache.line_separation;
		}
		if (p_ofs.y + off.y >= ctrl_size.height) {
			break;
		}
		const Size2 line_size = l.text_buf->get_line_size(line);
		if (p_ofs.y + off.y + line_size.y <= 0) {
			off.y += line_size.y;
			continue;
		}
		float width = l.text_buf->get_width();
		float length = line_size.x;
		
		line_count++;
		if (rtl) {
			off.x = p_width - l.offset.x - width;
			if (!lrtl && p_frame == main) { 
				off.x -= scroll_w;
			}
		} else {
			off.x = l.offset.x;
			if (lrtl && p_frame == main) { 
				off.x += scroll_w;
			}
		}