### 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)

}
	if (!f.is_valid()) {
		
		for (int i = p_start; i < p_end; i++) {
			if (p_sd->preserve_invalid || (p_sd->preserve_control && is_control(p_sd->text[i]))) {
				Glyph gl;
				gl.start = i + p_sd->start;
				gl.end = i + 1 + p_sd->start;
				gl.count = 1;
				gl.index = p_sd->text[i];
				gl.font_size = fs;
				gl.font_rid = RID();
				if (p_direction == HB_DIRECTION_RTL || p_direction == HB_DIRECTION_BTT) {
					gl.flags |= TextServer::GRAPHEME_IS_RTL;
				}
				if (p_sd->orientation == ORIENTATION_HORIZONTAL) {
					gl.advance = get_hex_code_box_size(fs, gl.index).x;
					p_sd->ascent = MAX(p_sd->ascent, get_hex_code_box_size(fs, gl.index).y);
				} else {
					gl.advance = get_hex_code_box_size(fs, gl.index).y;
					gl.y_off = get_hex_code_box_size(fs, gl.index).y;
					gl.x_off = -Math::round(get_hex_code_box_size(fs, gl.index).x * 0.5);
					p_sd->ascent = MAX(p_sd->ascent, Math::round(get_hex_code_box_size(fs, gl.index).x * 0.5));
					p_sd->descent = MAX(p_sd->descent, Math::round(get_hex_code_box_size(fs, gl.index).x * 0.5));
				}
				p_sd->width += gl.advance;
				p_sd->glyphs.push_back(gl);
			}
		}
		return;