### 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 
ERR_FAIL_COND(p_frame == nullptr);
	ERR_FAIL_COND(p_line < 0 || p_line >= (int)p_frame->lines.size());
	Line &l = p_frame->lines[p_line];
	MutexLock lock(l.text_buf->get_mutex());
	RID t = l.text_buf->get_rid();
	int spans = TS->shaped_get_span_count(t);
	for (int i = 0; i < spans; i++) {
		ItemText *it = reinterpret_cast<ItemText *>((uint64_t)TS->shaped_get_span_meta(t, i));
		if (it) {
			Ref<Font> font = p_base_font;
			int font_size = p_base_font_size;
			ItemFont *font_it = _find_font(it);
			if (font_it) {
				if (font_it->font.is_valid()) {
					font = font_it->font;
				}
				if (font_it->font_size > 0) {
					font_size = font_it->font_size;
				}
			}
			ItemFontSize *font_size_it = _find_font_size(it);
			if (font_size_it && font_size_it->font_size > 0) {
				font_size = font_size_it->font_size;
			}
			TS->shaped_set_span_update_font(t, i, font->get_rids(), font_size, font->get_opentype_features());
			for (int j = 0; j < TextServer::SPACING_MAX; j++) {
				TS->shaped_text_set_spacing(t, TextServer::SpacingType(j), font->get_spacing(TextServer::SpacingType(j)));
			}