### 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 
int l = p_from;
	int r = p_to;
	while (l < r) {
		int m = Math::floor(double(l + r) / 2.0);
		MutexLock lock(main->lines[m].text_buf->get_mutex());
		int ofs = _calculate_line_vertical_offset(main->lines[m]);
		if (ofs < p_vofs) {
			l = m + 1;
		} else {
			r = m;
		}
	}
	return MIN(l, (int)main->lines.size() - 1);
}
_FORCE_INLINE_ float RichTextLabel::_calculate_line_vertical_offset(const RichTextLabel::Line &line) const {