### 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 (width >= big_icon_width) {
			if (colors >= big_icon_cc) {
				big_icon_index = i;
				big_icon_width = width;
				big_icon_cc = colors;
			}
		}
	}
	ERR_FAIL_COND_MSG(big_icon_index == -1, "No valid icons found!");
	if (small_icon_index == -1) {
		WARN_PRINT("No small icon found, reusing " + itos(big_icon_width) + "x" + itos(big_icon_width) + " @" + itos(big_icon_cc) + " icon!");
		small_icon_index = big_icon_index;
		small_icon_cc = big_icon_cc;
	}
	
	DWORD bytecount_big = icon_dir->idEntries[big_icon_index].dwBytesInRes;
	Vector<uint8_t> data_big;
	data_big.resize(bytecount_big);
	pos = icon_dir->idEntries[big_icon_index].dwImageOffset;
	f->seek(pos);
	f->get_buffer((uint8_t *)&data_big.write[0], bytecount_big);
	HICON icon_big = CreateIconFromResource((PBYTE)&data_big.write[0], bytecount_big, TRUE, 0x00030000);
	ERR_FAIL_COND_MSG(!icon_big, "Could not create " + itos(big_icon_width) + "x" + itos(big_icon_width) + " @" + itos(big_icon_cc) + " icon, error: " + format_error_message(GetLastError()) + ".");
	
	DWORD bytecount_small = icon_dir->idEntries[small_icon_index].dwBytesInRes;
	Vector<uint8_t> data_small;
	data_small.resize(bytecount_small);
	pos = icon_dir->idEntries[small_icon_index].dwImageOffset;
	f->seek(pos);