### 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)

ERR_FAIL_COND_MSG((p_end >= 0xd800 && p_end <= 0xdfff) || (p_end > 0x10ffff), "Unicode parsing error: Invalid unicode codepoint " + String::num_int64(p_end, 16) + ".");
	MutexLock lock(fd->mutex);
	Vector2i size = _get_size_outline(fd, p_size);
	ERR_FAIL_COND(!_ensure_cache_for_size(fd, size));
	for (int64_t i = p_start; i <= p_end; i++) {
#ifdef MODULE_FREETYPE_ENABLED
		int32_t idx = FT_Get_Char_Index(fd->cache[size]->face, i);
		if (fd->cache[size]->face) {
			if (fd->msdf) {
				_ensure_glyph(fd, size, (int32_t)idx);
			} else {
				for (int aa = 0; aa < ((fd->antialiasing == FONT_ANTIALIASING_LCD) ? FONT_LCD_SUBPIXEL_LAYOUT_MAX : 1); aa++) {
					if ((fd->subpixel_positioning == SUBPIXEL_POSITIONING_ONE_QUARTER) || (fd->subpixel_positioning == SUBPIXEL_POSITIONING_AUTO && size.x <= SUBPIXEL_POSITIONING_ONE_QUARTER_MAX_SIZE)) {
						_ensure_glyph(fd, size, (int32_t)idx | (0 << 27) | (aa << 24));
						_ensure_glyph(fd, size, (int32_t)idx | (1 << 27) | (aa << 24));
						_ensure_glyph(fd, size, (int32_t)idx | (2 << 27) | (aa << 24));
						_ensure_glyph(fd, size, (int32_t)idx | (3 << 27) | (aa << 24));
					} else if ((fd->subpixel_positioning == SUBPIXEL_POSITIONING_ONE_HALF) || (fd->subpixel_positioning == SUBPIXEL_POSITIONING_AUTO && size.x <= SUBPIXEL_POSITIONING_ONE_HALF_MAX_SIZE)) {
						_ensure_glyph(fd, size, (int32_t)idx | (1 << 27) | (aa << 24));
						_ensure_glyph(fd, size, (int32_t)idx | (0 << 27) | (aa << 24));
					} else {
						_ensure_glyph(fd, size, (int32_t)idx | (aa << 24));
					}
				}
			}
		}
#endif
	}
}
void TextServerAdvanced::_font_render_glyph(const RID &p_font_rid, const Vector2i &p_size, int64_t p_index) {