### 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
ofs.y += s.y;
			} break;
			case DOCK_SLOT_LEFT_UR: {
				ofs.x += s.x;
			} break;
			case DOCK_SLOT_LEFT_BR: {
				ofs += s;
			} break;
			case DOCK_SLOT_RIGHT_UL: {
				ofs.x += s.x * 4;
			} break;
			case DOCK_SLOT_RIGHT_BL: {
				ofs.x += s.x * 4;
				ofs.y += s.y;
			} break;
			case DOCK_SLOT_RIGHT_UR: {
				ofs.x += s.x * 4;
				ofs.x += s.x;
			} break;
			case DOCK_SLOT_RIGHT_BR: {
				ofs.x += s.x * 4;
				ofs += s;
			} break;
		}
		Rect2 r(ofs, s);
		dock_select_rect[i] = r;
		r.position += Vector2(2, 5);
		r.size -= Vector2(4, 7);
		if (i == dock_select_rect_over_idx) {
			dock_select->draw_rect(r, used_selected);