### 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 
ItemFont *font_it = _find_font(current);
				if (font_it) {
					if (font_it->font.is_valid()) {
						font = font_it->font;
						def_font = font_it->def_font;
					}
				}
				Dictionary features;
				for (int i = 0; i < subtag.size(); i++) {
					Vector<String> subtag_a = subtag[i].split("=");
					_normalize_subtags(subtag_a);
					if (subtag_a.size() == 2) {
						features[TS->name_to_tag(subtag_a[0])] = subtag_a[1].to_int();
					} else if (subtag_a.size() == 1) {
						features[TS->name_to_tag(subtag_a[0])] = 1;
					}
				}
				Ref<FontVariation> fc;
				fc.instantiate();
				fc->set_base_font(font);
				fc->set_opentype_features(features);
				if (def_font != CUSTOM_FONT) {
					_push_def_font_var(def_font, fc);
				} else {
					push_font(fc);
				}
			}
			pos = brk_end + 1;
			tag_stack.push_front(tag.substr(0, value_pos));
		} else if (tag.begins_with("font=")) {