### 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 (windows[window_id].last_pressure_update < 10) {
					windows[window_id].last_pressure_update++;
				} else {
					windows[window_id].last_tilt = Vector2();
					windows[window_id].last_pressure = (wParam & MK_LBUTTON) ? 1.0f : 0.0f;
					windows[window_id].last_pen_inverted = false;
				}
			} else {
				windows[window_id].last_tilt = Vector2();
				windows[window_id].last_pressure = (wParam & MK_LBUTTON) ? 1.0f : 0.0f;
				windows[window_id].last_pen_inverted = false;
			}
			mm->set_pressure(windows[window_id].last_pressure);
			mm->set_tilt(windows[window_id].last_tilt);
			mm->set_pen_inverted(windows[window_id].last_pen_inverted);
			mm->set_button_mask(last_button_state);
			mm->set_position(Vector2(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)));
			mm->set_global_position(Vector2(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)));
			if (mouse_mode == MOUSE_MODE_CAPTURED) {
				Point2i c(windows[window_id].width / 2, windows[window_id].height / 2);
				old_x = c.x;
				old_y = c.y;
				if (mm->get_position() == c) {
					center = c;
					return 0;
				}
				Point2i ncenter = mm->get_position();
				center = ncenter;
				POINT pos = { (int)c.x, (int)c.y };
				ClientToScreen(windows[window_id].hWnd, &pos);