### 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)

case WM_RBUTTONDOWN: {
					mb->set_pressed(true);
					mb->set_button_index(MouseButton::RIGHT);
				} break;
				case WM_RBUTTONUP: {
					mb->set_pressed(false);
					mb->set_button_index(MouseButton::RIGHT);
				} break;
				case WM_LBUTTONDBLCLK: {
					mb->set_pressed(true);
					mb->set_button_index(MouseButton::LEFT);
					mb->set_double_click(true);
				} break;
				case WM_RBUTTONDBLCLK: {
					mb->set_pressed(true);
					mb->set_button_index(MouseButton::RIGHT);
					mb->set_double_click(true);
				} break;
				case WM_MBUTTONDBLCLK: {
					mb->set_pressed(true);
					mb->set_button_index(MouseButton::MIDDLE);
					mb->set_double_click(true);
				} break;
				case WM_MOUSEWHEEL: {
					mb->set_pressed(true);
					int motion = (short)HIWORD(wParam);
					if (!motion) {
						return 0;
					}
					if (motion > 0) {