### Godot version

4.1 rc3

### System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 30.0.15.1403) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

### Issue description

This™
![image](https://github.com/godotengine/godot/assets/2223172/cb33110f-a5b0-400a-951f-3fa425f05714)

It can still happen, but it's more difficult to trigger.

### Steps to reproduce

1. Create a new scene with a Control node
2. Add Theme to the Control
3. Open Theme Editor
4. Clear the `theme` property in Control
5. Save, with Theme Editor opened
6. Restart

### Minimal reproduction project

N/A
help_menu->set_item_icon(help_menu->get_item_index(HELP_QA), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_REPORT_A_BUG), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_COPY_SYSTEM_INFO), gui_base->get_theme_icon(SNAME("ActionCopy"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_SUGGEST_A_FEATURE), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_SEND_DOCS_FEEDBACK), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_COMMUNITY), gui_base->get_theme_icon(SNAME("ExternalLink"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_ABOUT), gui_base->get_theme_icon(SNAME("Godot"), SNAME("EditorIcons")));
			help_menu->set_item_icon(help_menu->get_item_index(HELP_SUPPORT_GODOT_DEVELOPMENT), gui_base->get_theme_icon(SNAME("Heart"), SNAME("EditorIcons")));
			for (int i = 0; i < main_editor_buttons.size(); i++) {
				main_editor_buttons.write[i]->add_theme_font_override("font", gui_base->get_theme_font(SNAME("main_button_font"), SNAME("EditorFonts")));
				main_editor_buttons.write[i]->add_theme_font_size_override("font_size", gui_base->get_theme_font_size(SNAME("main_button_font_size"), SNAME("EditorFonts")));
			}
			HashSet<String> updated_textfile_extensions;
			bool extensions_match = true;
			const Vector<String> textfile_ext = ((String)(EDITOR_GET("docks/filesystem/textfile_extensions"))).split(",", false);
			for (const String &E : textfile_ext) {
				updated_textfile_extensions.insert(E);
				if (extensions_match && !textfile_extensions.has(E)) {
					extensions_match = false;
				}
			}
			if (!extensions_match || updated_textfile_extensions.size() < textfile_extensions.size()) {
				textfile_extensions = updated_textfile_extensions;
				EditorFileSystem::get_singleton()->scan();
			}
			_update_update_spinner();
		} break;
	}
}
void EditorNode::_update_update_spinner() {