### 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)

} else {
				
				wd.layered_window = false;
				DWM_BLURBEHIND bb;
				ZeroMemory(&bb, sizeof(bb));
				HRGN hRgn = CreateRectRgn(0, 0, -1, -1);
				bb.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
				bb.hRgnBlur = hRgn;
				bb.fEnable = FALSE;
				DwmEnableBlurBehindWindow(wd.hWnd, &bb);
			}
		} break;
		case WINDOW_FLAG_NO_FOCUS: {
			wd.no_focus = p_enabled;
			_update_window_style(p_window);
		} break;
		case WINDOW_FLAG_MOUSE_PASSTHROUGH: {
			wd.mpass = p_enabled;
			_update_window_mouse_passthrough(p_window);
		} break;
		case WINDOW_FLAG_POPUP: {
			ERR_FAIL_COND_MSG(p_window == MAIN_WINDOW_ID, "Main window can't be popup.");
			ERR_FAIL_COND_MSG(IsWindowVisible(wd.hWnd) && (wd.is_popup != p_enabled), "Popup flag can't changed while window is opened.");
			wd.is_popup = p_enabled;
		} break;
		default:
			break;
	}
}
bool DisplayServerWindows::window_get_flag(WindowFlags p_flag, WindowID p_window) const {