### 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 (width + (((above_min_char_threshold && add_ellipsis) || enforce_ellipsis) ? ellipsis_width : 0) <= p_width) {
					if (cut_per_word && above_min_char_threshold) {
						if ((sd_glyphs[i].flags & GRAPHEME_IS_BREAK_SOFT) == GRAPHEME_IS_BREAK_SOFT) {
							last_valid_cut = i;
							found = true;
						}
					} else {
						last_valid_cut = i;
						found = true;
					}
					if (found) {
						trim_pos = last_valid_cut;
						if (add_ellipsis && (above_min_char_threshold || enforce_ellipsis) && width - ellipsis_width <= p_width) {
							ellipsis_pos = trim_pos;
						}
						
					}
				}
			}
			if (is_rtl) {
				width -= sd_glyphs[i].advance * sd_glyphs[i].repeat;
			}
		}
	}
	sd->overrun_trim_data.trim_pos = trim_pos;
	sd->overrun_trim_data.ellipsis_pos = ellipsis_pos;
	if (trim_pos == 0 && enforce_ellipsis && add_ellipsis) {
		sd->overrun_trim_data.ellipsis_pos = 0;
	}
	if ((trim_pos >= 0 && sd->width > p_width) || enforce_ellipsis) {