### 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 (fd->msdf) {
					Point2 cpos = p_pos;
					cpos += gl.rect.position * (double)p_size / (double)fd->msdf_source_size;
					Size2 csize = gl.rect.size * (double)p_size / (double)fd->msdf_source_size;
					RenderingServer::get_singleton()->canvas_item_add_msdf_texture_rect_region(p_canvas, Rect2(cpos, csize), texture, gl.uv_rect, modulate, p_outline_size, fd->msdf_range, (double)p_size / (double)fd->msdf_source_size);
				} else {
					Point2 cpos = p_pos;
					double scale = _font_get_scale(p_font_rid, p_size);
					if ((fd->subpixel_positioning == SUBPIXEL_POSITIONING_ONE_QUARTER) || (fd->subpixel_positioning == SUBPIXEL_POSITIONING_AUTO && size.x <= SUBPIXEL_POSITIONING_ONE_QUARTER_MAX_SIZE)) {
						cpos.x = cpos.x + 0.125;
					} else if ((fd->subpixel_positioning == SUBPIXEL_POSITIONING_ONE_HALF) || (fd->subpixel_positioning == SUBPIXEL_POSITIONING_AUTO && size.x <= SUBPIXEL_POSITIONING_ONE_HALF_MAX_SIZE)) {
						cpos.x = cpos.x + 0.25;
					}
					if (scale == 1.0) {
						cpos.y = Math::floor(cpos.y);
						cpos.x = Math::floor(cpos.x);
					}
					cpos += gl.rect.position;
					Size2 csize = gl.rect.size;
					if (lcd_aa) {
						RenderingServer::get_singleton()->canvas_item_add_lcd_texture_rect_region(p_canvas, Rect2(cpos, csize), texture, gl.uv_rect, modulate);
					} else {
						RenderingServer::get_singleton()->canvas_item_add_texture_rect_region(p_canvas, Rect2(cpos, csize), texture, gl.uv_rect, modulate, false, false);
					}
				}
			}
		}
	}
}
bool TextServerAdvanced::_font_is_language_supported(const RID &p_font_rid, const String &p_language) const {