### 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 ((int)p_frame->lines.size() - 1 <= p_frame->first_invalid_line) {
		p_frame->first_invalid_line = (int)p_frame->lines.size() - 1;
	}
}
void RichTextLabel::add_text(const String &p_text) {
	_stop_thread();
	MutexLock data_lock(data_mutex);
	if (current->type == ITEM_TABLE) {
		return; 
	}
	int pos = 0;
	while (pos < p_text.length()) {
		int end = p_text.find("\n", pos);
		String line;
		bool eol = false;
		if (end == -1) {
			end = p_text.length();
		} else {
			eol = true;
		}
		if (pos == 0 && end == p_text.length()) {
			line = p_text;
		} else {