### 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)

0, 0, 
				0, 
				AnyPropertyType, 
				&type, 
				&format, 
				&len, &bytes_left, 
				&data);
		if (data) {
			XFree(data);
		}
		if (type == XInternAtom(x11_display, "INCR", 0)) {
			
			DEBUG_LOG_X11("INCR selection started.\n");
			LocalVector<uint8_t> incr_data;
			uint32_t data_size = 0;
			bool success = false;
			
			XDeleteProperty(x11_display, x11_window, type);
			
			bool done = false;
			while (!done) {
				if (!_wait_for_events()) {
					
					break;
				}
				
				XEvent ev;
				while (XCheckIfEvent(x11_display, &ev, _predicate_clipboard_incr, nullptr)) {
					result = XGetWindowProperty(x11_display, x11_window,
							selection,