### 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)

}
				gloff.x += glyphs[i].advance;
			}
		}
		Vector2 fbg_line_off = off + p_ofs;
		
		Vector2i chr_range = TS->shaped_text_get_range(rid);
		_draw_fbg_boxes(ci, rid, fbg_line_off, it_from, it_to, chr_range.x, chr_range.y, 0);
		
		Color selection_bg = theme_cache.selection_color;
		int sel_start = -1;
		int sel_end = -1;
		if (selection.active && (selection.from_frame->lines[selection.from_line].char_offset + selection.from_char) <= (l.char_offset + TS->shaped_text_get_range(rid).y) && (selection.to_frame->lines[selection.to_line].char_offset + selection.to_char) >= (l.char_offset + TS->shaped_text_get_range(rid).x)) {
			sel_start = MAX(TS->shaped_text_get_range(rid).x, (selection.from_frame->lines[selection.from_line].char_offset + selection.from_char) - l.char_offset);
			sel_end = MIN(TS->shaped_text_get_range(rid).y, (selection.to_frame->lines[selection.to_line].char_offset + selection.to_char) - l.char_offset);
			Vector<Vector2> sel = TS->shaped_text_get_selection(rid, sel_start, sel_end);
			for (int i = 0; i < sel.size(); i++) {
				Rect2 rect = Rect2(sel[i].x + p_ofs.x + off.x, p_ofs.y + off.y - TS->shaped_text_get_ascent(rid), sel[i].y - sel[i].x, TS->shaped_text_get_size(rid).y);
				RenderingServer::get_singleton()->canvas_item_add_rect(ci, rect, selection_bg);
			}
		}
		Vector2 ul_start;
		bool ul_started = false;
		Color ul_color;
		Vector2 dot_ul_start;
		bool dot_ul_started = false;
		Color dot_ul_color;
		Vector2 st_start;
		bool st_started = false;
		Color st_color;