### 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 
if (visible_chars_behavior != p_behavior) {
		_stop_thread();
		visible_chars_behavior = p_behavior;
		main->first_invalid_line.store(0); 
		_validate_line_caches();
		queue_redraw();
	}
}
void RichTextLabel::set_visible_characters(int p_visible) {
	if (visible_characters != p_visible) {
		_stop_thread();
		visible_characters = p_visible;
		if (p_visible == -1) {
			visible_ratio = 1;
		} else {
			int total_char_count = get_total_character_count();
			if (total_char_count > 0) {
				visible_ratio = (float)p_visible / (float)total_char_count;
			}
		}
		if (visible_chars_behavior == TextServer::VC_CHARS_BEFORE_SHAPING) {
			main->first_invalid_line.store(0); 
			_validate_line_caches();
		}
		queue_redraw();
	}
}
int RichTextLabel::get_visible_characters() const {