Python 3.10: segfault due to invalid pointer

On 3.10 alpha 4, pillow fail to run and segfault with "invalid pointer". All projects depending on Pillow also fail to build.

```
python3 -c 'from PIL import Image'
free(): invalid pointer
Aborted (core dumped)
```

### What are your OS, Python and Pillow versions?

* OS: Fedora Linux Rawhide
* Python: 3.10 alpha4
* Pillow: 8.1.0
