### 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 (bHandled) {
				CloseTouchInputHandle((HTOUCHINPUT)lParam);
				return 0;
			}
		} break;
		case WM_DEVICECHANGE: {
			joypad->probe_joypads();
		} break;
		case WM_DESTROY: {
			Input::get_singleton()->flush_buffered_events();
		} break;
		case WM_SETCURSOR: {
			if (LOWORD(lParam) == HTCLIENT) {
				if (windows[window_id].window_has_focus && (mouse_mode == MOUSE_MODE_HIDDEN || mouse_mode == MOUSE_MODE_CAPTURED || mouse_mode == MOUSE_MODE_CONFINED_HIDDEN)) {
					
					if (hCursor == nullptr) {
						hCursor = SetCursor(nullptr);
					} else {
						SetCursor(nullptr);
					}
				} else {
					if (hCursor != nullptr) {
						CursorShape c = cursor_shape;
						cursor_shape = CURSOR_MAX;
						cursor_set_shape(c);
						hCursor = nullptr;
					}
				}