### Godot version

master ([06ccbfe](https://github.com/godotengine/godot/commit/06ccbfe8eec6e840db3df2360dc2804386f940b8))

### System information

PopOS 22.04

### Issue description

Sometimes the doc page is broken when the engine is closed and then restarted.
Closing the doc and opening it again fixes it.

![2023-05-27_22-15](https://github.com/godotengine/godot/assets/3624853/ed202a55-03e8-420a-bc1c-ccfc7f7cd02a)


### Steps to reproduce

- Open a documentation page for any node
- Restart Godot

### Minimal reproduction project

NA

EDIT : Added the commit hash @Calinou 
_stop_thread();
	MutexLock data_lock(data_mutex);
	main->_clear_children();
	current = main;
	current_frame = main;
	main->lines.clear();
	main->lines.resize(1);
	main->first_invalid_line.store(0);
	selection.click_frame = nullptr;
	selection.click_item = nullptr;
	deselect();
	current_idx = 1;
	current_char_ofs = 0;
	if (scroll_follow) {
		scroll_following = true;
	}
	if (fit_content) {
		update_minimum_size();
	}
}
void RichTextLabel::set_tab_size(int p_spaces) {
	if (tab_size == p_spaces) {
		return;
	}
	_stop_thread();
	tab_size = p_spaces;
	main->first_resized_line.store(0);
	queue_redraw();
}
int RichTextLabel::get_tab_size() const {