### Godot version

Godot Engine v4.0.stable.official.92bee43ad

### System information

Windows 10

### Issue description

The documentation states that passing ```null``` into the image parameter of ```set_custom_mouse_cursor``` will change it back to the system cursor, however I find that it removes the cursor's image entirely, rather than setting it to the system's cursor.


### Steps to reproduce

```var isimage = false
var theimage = load("res://final.png")

func _on_my_button_pressed():
    if isimage == false:
        Input.set_custom_mouse_cursor(theimage, Input.CURSOR_ARROW, Vector2(16,16))
        isimage = true
        
    else:
        Input.set_custom_mouse_cursor(null)
        isimage = false```

When the button is pressed, the cursor is meant to change to the new cursor. When it has been pressed a second time, it changes back to the default cursor. However, upon pressing it a second time, it simply disappears. The cursor becomes visible again when the cursor exits and re-enters the window.

### Minimal reproduction project

[null mouse.zip](https://github.com/godotengine/godot/files/10901969/null.mouse.zip)

}
		} break;
		case WM_DROPFILES: {
			HDROP hDropInfo = (HDROP)wParam;
			const int buffsize = 4096;
			WCHAR buf[buffsize];
			int fcount = DragQueryFileW(hDropInfo, 0xFFFFFFFF, nullptr, 0);
			Vector<String> files;
			for (int i = 0; i < fcount; i++) {
				DragQueryFileW(hDropInfo, i, buf, buffsize);
				String file = String::utf16((const char16_t *)buf);
				files.push_back(file);
			}
			if (files.size() && !windows[window_id].drop_files_callback.is_null()) {
				Variant v = files;
				Variant *vp = &v;
				Variant ret;
				Callable::CallError ce;
				windows[window_id].drop_files_callback.callp((const Variant **)&vp, 1, ret, ce);
			}
		} break;
		default: {
			if (user_proc) {
				return CallWindowProcW(user_proc, hWnd, uMsg, wParam, lParam);
			}
		}
	}
	return DefWindowProcW(hWnd, uMsg, wParam, lParam);
}
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {