### 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)

old_x = mm->get_position().x;
			old_y = mm->get_position().y;
			if (windows[window_id].window_has_focus || window_get_active_popup() == window_id) {
				Input::get_singleton()->parse_input_event(mm);
			}
			return 0; 
		} break;
		case WM_MOUSEMOVE: {
			if (windows[window_id].block_mm) {
				break;
			}
			if (mouse_mode == MOUSE_MODE_CAPTURED && use_raw_input) {
				break;
			}
			if (Input::get_singleton()->is_emulating_mouse_from_touch()) {
				
				LPARAM extra = GetMessageExtraInfo();
				if (IsTouchEvent(extra)) {
					break;
				}
			}
			DisplayServer::WindowID over_id = get_window_at_screen_position(mouse_get_position());
			if (windows.has(over_id) && !Rect2(window_get_position(over_id), Point2(windows[over_id].width, windows[over_id].height)).has_point(mouse_get_position())) {
				
				over_id = INVALID_WINDOW_ID;
			}
			if (window_mouseover_id != over_id) {
				
				if (mouse_mode != MOUSE_MODE_CAPTURED) {
					if (window_mouseover_id != INVALID_WINDOW_ID && windows.has(window_mouseover_id)) {