### 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 (!is_transparent(c)) {
			pc = c;
		}
		i++;
	}
	return kashida_pos;
}
bool TextServerAdvanced::_shaped_text_update_justification_ops(const RID &p_shaped) {
	ShapedTextDataAdvanced *sd = shaped_owner.get_or_null(p_shaped);
	ERR_FAIL_COND_V(!sd, false);
	MutexLock lock(sd->mutex);
	if (!sd->valid) {
		_shaped_text_shape(p_shaped);
	}
	if (!sd->line_breaks_valid) {
		_shaped_text_update_breaks(p_shaped);
	}
	if (sd->justification_ops_valid) {
		return true; 
	}
	const UChar *data = sd->utf16.get_data();
	int data_size = sd->utf16.length();
	if (!sd->js_ops_valid) {
		sd->jstops.clear();
		
		UErrorCode err = U_ZERO_ERROR;
		UBreakIterator *bi = ubrk_open(UBRK_WORD, "", data, data_size, &err);
		if (U_FAILURE(err)) {