### 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)

double old_adv = gl.advance;
					double new_advance;
					if ((gl.flags & GRAPHEME_IS_VIRTUAL) == GRAPHEME_IS_VIRTUAL) {
						new_advance = MAX(gl.advance + delta_width_per_space, 0.0);
					} else {
						new_advance = MAX(gl.advance + delta_width_per_space, 0.1 * gl.font_size);
					}
					gl.advance = new_advance;
					adv_remain += (new_advance - gl.advance);
					if (adv_remain >= 1.0) {
						gl.advance++;
						adv_remain -= 1.0;
					} else if (adv_remain <= -1.0) {
						gl.advance = MAX(gl.advance - 1, 0);
						adv_remain -= 1.0;
					}
					justification_width += (gl.advance - old_adv);
				}
			}
		}
	}
	if (Math::floor(p_width) < Math::floor(justification_width)) {
		sd->fit_width_minimum_reached = true;
	}
	if (!p_jst_flags.has_flag(JUSTIFICATION_CONSTRAIN_ELLIPSIS)) {
		sd->width = justification_width;
	}
	return Math::ceil(justification_width);
}
double TextServerAdvanced::_shaped_text_tab_align(const RID &p_shaped, const PackedFloat32Array &p_tab_stops) {