### 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 (sd->para_direction == DIRECTION_LTR) {
					start_pos = i;
					
				} else {
					end_pos = i;
					
				}
			}
		}
	}
	double justification_width;
	if (p_jst_flags.has_flag(JUSTIFICATION_CONSTRAIN_ELLIPSIS)) {
		if (sd->overrun_trim_data.trim_pos >= 0) {
			if (sd->para_direction == DIRECTION_RTL) {
				start_pos = sd->overrun_trim_data.trim_pos;
			} else {
				end_pos = sd->overrun_trim_data.trim_pos;
			}
			justification_width = sd->width_trimmed;
		} else {
			return Math::ceil(sd->width);
		}
	} else {
		justification_width = sd->width;
	}
	if (p_jst_flags.has_flag(JUSTIFICATION_TRIM_EDGE_SPACES)) {
		
		while ((start_pos < end_pos) && ((sd->glyphs[start_pos].flags & GRAPHEME_IS_SPACE) == GRAPHEME_IS_SPACE || (sd->glyphs[start_pos].flags & GRAPHEME_IS_BREAK_HARD) == GRAPHEME_IS_BREAK_HARD || (sd->glyphs[start_pos].flags & GRAPHEME_IS_BREAK_SOFT) == GRAPHEME_IS_BREAK_SOFT)) {
			justification_width -= sd->glyphs[start_pos].advance * sd->glyphs[start_pos].repeat;
			sd->glyphs.write[start_pos].advance = 0;