### Godot version

v4.0.beta17.mono.official [c40020513]

### System information

Window 11, Forward+, GTX 1060

### Issue description

Adding two theme variations in a row result to a  crash.

https://user-images.githubusercontent.com/93253123/217037249-1ce1d56d-beb6-4435-83ad-9f8a07fe0e96.mp4



### Steps to reproduce

1. Create a project.
2. Create a theme.
3. Double click to go in the theme editor.
4. Click on manage items buttons.
5. In the add type field type a name to add a type.
6. type another name to add a second type.
7. Crash.

### Minimal reproduction project

[ThemeVariationCrash.zip](https://github.com/godotengine/godot/files/10665863/ThemeVariationCrash.zip)

select_full_icons_button->set_visible(false);
		deselect_all_icons_button->set_visible(false);
		select_icons_warning_hb->set_visible(false);
	}
	if (stylebox_amount > 0) {
		Array arr;
		arr.push_back(stylebox_amount);
		select_styleboxes_label->set_text(TTRN("1 stylebox", "{num} styleboxes", stylebox_amount).format(arr, "{num}"));
		select_all_styleboxes_button->set_visible(true);
		select_full_styleboxes_button->set_visible(true);
		deselect_all_styleboxes_button->set_visible(true);
	} else {
		select_styleboxes_label->set_text(TTR("No styleboxes found."));
		select_all_styleboxes_button->set_visible(false);
		select_full_styleboxes_button->set_visible(false);
		deselect_all_styleboxes_button->set_visible(false);
	}
}
void ThemeItemImportTree::_toggle_type_items(bool p_collapse) {
	TreeItem *root = import_items_tree->get_root();
	if (!root) {
		return;
	}
	TreeItem *type_node = root->get_first_child();
	while (type_node) {
		type_node->set_collapsed(p_collapse);
		type_node = type_node->get_next();
	}
}
void ThemeItemImportTree::_filter_text_changed(const String &p_value) {