### 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)

if (p_target == XInternAtom(x11_display, "TARGETS", 0)) {
		
		Atom data[9];
		data[0] = XInternAtom(x11_display, "TARGETS", 0);
		data[1] = XInternAtom(x11_display, "SAVE_TARGETS", 0);
		data[2] = XInternAtom(x11_display, "MULTIPLE", 0);
		data[3] = XInternAtom(x11_display, "UTF8_STRING", 0);
		data[4] = XInternAtom(x11_display, "COMPOUND_TEXT", 0);
		data[5] = XInternAtom(x11_display, "TEXT", 0);
		data[6] = XA_STRING;
		data[7] = XInternAtom(x11_display, "text/plain;charset=utf-8", 0);
		data[8] = XInternAtom(x11_display, "text/plain", 0);
		XChangeProperty(x11_display,
				p_requestor,
				p_property,
				XA_ATOM,
				32,
				PropModeReplace,
				(unsigned char *)&data,
				sizeof(data) / sizeof(data[0]));