### 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)

}
	}
	int32_t dot_gl_idx = dot_gl_font_rid.is_valid() ? _font_get_glyph_index(dot_gl_font_rid, last_gl_font_size, '.', 0) : -10;
	Vector2 dot_adv = dot_gl_font_rid.is_valid() ? _font_get_glyph_advance(dot_gl_font_rid, last_gl_font_size, dot_gl_idx) : Vector2();
	int32_t whitespace_gl_idx = whitespace_gl_font_rid.is_valid() ? _font_get_glyph_index(whitespace_gl_font_rid, last_gl_font_size, ' ', 0) : -10;
	Vector2 whitespace_adv = whitespace_gl_font_rid.is_valid() ? _font_get_glyph_advance(whitespace_gl_font_rid, last_gl_font_size, whitespace_gl_idx) : Vector2();
	int ellipsis_width = 0;
	if (add_ellipsis && whitespace_gl_font_rid.is_valid()) {
		ellipsis_width = 3 * dot_adv.x + sd->extra_spacing[SPACING_GLYPH] + (cut_per_word ? whitespace_adv.x : 0);
	}
	int ell_min_characters = 6;
	double width = sd->width;
	bool is_rtl = sd->para_direction == DIRECTION_RTL;
	int trim_pos = (is_rtl) ? sd_size : 0;
	int ellipsis_pos = (enforce_ellipsis) ? 0 : -1;
	int last_valid_cut = 0;
	bool found = false;
	int glyphs_from = (is_rtl) ? 0 : sd_size - 1;
	int glyphs_to = (is_rtl) ? sd_size - 1 : -1;
	int glyphs_delta = (is_rtl) ? +1 : -1;
	if (enforce_ellipsis && (width + ellipsis_width <= p_width)) {
		trim_pos = -1;
		ellipsis_pos = (is_rtl) ? 0 : sd_size;
	} else {
		for (int i = glyphs_from; i != glyphs_to; i += glyphs_delta) {
			if (!is_rtl) {
				width -= sd_glyphs[i].advance * sd_glyphs[i].repeat;
			}
			if (sd_glyphs[i].count > 0) {
				bool above_min_char_threshold = ((is_rtl) ? sd_size - 1 - i : i) >= ell_min_characters;