### 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)

int64_t kashida_pos = -1;
	int8_t priority = 100;
	int64_t i = p_start;
	char32_t pc = 0;
	while ((p_end > p_start) && is_transparent(p_data[p_end - 1])) {
		p_end--;
	}
	while (i < p_end) {
		uint32_t c = p_data[i];
		if (c == 0x0640) {
			kashida_pos = i;
			priority = 0;
		}
		if (priority >= 1 && i < p_end - 1) {
			if (is_seen_sad(c) && (p_data[i + 1] != 0x200c)) {
				kashida_pos = i;
				priority = 1;
			}
		}
		if (priority >= 2 && i > p_start) {
			if (is_teh_marbuta(c) || is_dal(c) || (is_heh(c) && i == p_end - 1)) {
				if (is_connected_to_prev(c, pc)) {
					kashida_pos = i - 1;
					priority = 2;
				}
			}
		}
		if (priority >= 3 && i > p_start) {
			if (is_alef(c) || ((is_lam(c) || is_tah(c) || is_kaf(c) || is_gaf(c)) && i == p_end - 1)) {