### 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)

gl.index = glyph_info[i].codepoint;
			if (gl.index != 0) {
				_ensure_glyph(fd, fss, gl.index | mod);
				if (p_sd->orientation == ORIENTATION_HORIZONTAL) {
					if (subpos) {
						gl.advance = (double)glyph_pos[i].x_advance / (64.0 / scale) + ea;
					} else {
						gl.advance = Math::round((double)glyph_pos[i].x_advance / (64.0 / scale) + ea);
					}
				} else {
					gl.advance = -Math::round((double)glyph_pos[i].y_advance / (64.0 / scale));
				}
				if (subpos) {
					gl.x_off = (double)glyph_pos[i].x_offset / (64.0 / scale);
				} else {
					gl.x_off = Math::round((double)glyph_pos[i].x_offset / (64.0 / scale));
				}
				gl.y_off = -Math::round((double)glyph_pos[i].y_offset / (64.0 / scale));
			}
			if (!last_run || i < glyph_count - 1) {
				
				if (sp_sp && is_whitespace(p_sd->text[glyph_info[i].cluster])) {
					gl.advance += sp_sp;
				} else {
					gl.advance += sp_gl;
				}
			}
			if (p_sd->preserve_control) {
				last_cluster_valid = last_cluster_valid && ((glyph_info[i].codepoint != 0) || (p_sd->text[glyph_info[i].cluster] == 0x0009) || (u_isblank(p_sd->text[glyph_info[i].cluster]) && (gl.advance != 0)) || (!u_isblank(p_sd->text[glyph_info[i].cluster]) && is_linebreak(p_sd->text[glyph_info[i].cluster])));
			} else {