### 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)

sd->js_ops_valid = true;
	}
	sd->sort_valid = false;
	sd->glyphs_logical.clear();
	Glyph *sd_glyphs = sd->glyphs.ptrw();
	int sd_size = sd->glyphs.size();
	if (!sd->jstops.is_empty()) {
		for (int i = 0; i < sd_size; i++) {
			if (sd_glyphs[i].count > 0) {
				char32_t c = sd->text[sd_glyphs[i].start - sd->start];
				if (c == 0x0640 && sd_glyphs[i].start == sd_glyphs[i].end - 1) {
					sd_glyphs[i].flags |= GRAPHEME_IS_ELONGATION;
				}
				if (sd->jstops.has(sd_glyphs[i].start)) {
					if (c == 0xfffc) {
						continue;
					}
					if (sd->jstops[sd_glyphs[i].start]) {
						if (c != 0x0640) {
							if (sd_glyphs[i].font_rid != RID()) {
								Glyph gl = _shape_single_glyph(sd, 0x0640, HB_SCRIPT_ARABIC, HB_DIRECTION_RTL, sd->glyphs[i].font_rid, sd->glyphs[i].font_size);
								if ((sd_glyphs[i].flags & GRAPHEME_IS_VALID) == GRAPHEME_IS_VALID) {
#if HB_VERSION_ATLEAST(5, 1, 0)
									if ((i > 0) && ((sd_glyphs[i - 1].flags & GRAPHEME_IS_SAFE_TO_INSERT_TATWEEL) != GRAPHEME_IS_SAFE_TO_INSERT_TATWEEL)) {
										continue;
									}
#endif
									gl.start = sd_glyphs[i].start;
									gl.end = sd_glyphs[i].end;
									gl.repeat = 0;