### 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)

static const char *target_type = "text/uri-list";
	for (int i = 0; i < p_count; i++) {
		Atom atom = p_list[i];
		if (atom != None && get_atom_name(p_display, atom) == target_type) {
			return atom;
		}
	}
	return None;
}
static Atom pick_target_from_atoms(Display *p_disp, Atom p_t1, Atom p_t2, Atom p_t3) {
	static const char *target_type = "text/uri-list";
	if (p_t1 != None && get_atom_name(p_disp, p_t1) == target_type) {
		return p_t1;
	}
	if (p_t2 != None && get_atom_name(p_disp, p_t2) == target_type) {
		return p_t2;
	}
	if (p_t3 != None && get_atom_name(p_disp, p_t3) == target_type) {
		return p_t3;
	}
	return None;
}
void DisplayServerX11::_get_key_modifier_state(unsigned int p_x11_state, Ref<InputEventWithModifiers> state) {