### 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)

const ::XIMStyle preedit = XIMPreeditArea | XIMPreeditCallbacks | XIMPreeditPosition | XIMPreeditNothing | XIMPreeditNone;
	const ::XIMStyle status = XIMStatusArea | XIMStatusCallbacks | XIMStatusNothing | XIMStatusNone;
	::XIMStyle a = p_style_a & preedit;
	::XIMStyle b = p_style_b & preedit;
	if (a != b) {
		
		if ((a | b) & XIMPreeditCallbacks) {
			return a == XIMPreeditCallbacks ? p_style_a : p_style_b;
		} else if ((a | b) & XIMPreeditPosition) {
			return a == XIMPreeditPosition ? p_style_a : p_style_b;
		} else if ((a | b) & XIMPreeditArea) {
			return a == XIMPreeditArea ? p_style_a : p_style_b;
		} else if ((a | b) & XIMPreeditNothing) {
			return a == XIMPreeditNothing ? p_style_a : p_style_b;
		}
	} else {
		
		a = p_style_a & status;
		b = p_style_b & status;
		if ((a | b) & XIMStatusCallbacks) {
			return a == XIMStatusCallbacks ? p_style_a : p_style_b;
		} else if ((a | b) & XIMStatusArea) {
			return a == XIMStatusArea ? p_style_a : p_style_b;
		} else if ((a | b) & XIMStatusNothing) {
			return a == XIMStatusNothing ? p_style_a : p_style_b;
		}
	}
	return p_style_a;
}
DisplayServerX11::DisplayServerX11(const String &p_rendering_driver, WindowMode p_mode, VSyncMode p_vsync_mode, uint32_t p_flags, const Vector2i *p_position, const Vector2i &p_resolution, int p_screen, Error &r_error) {