qed leaked clusters

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1806196
Reported by 'Коренберг Марк' on 2018-12-01 :

There are examples of two QED files which AFAIK does not have any errors
both. But `qemu-img check` says that one of them has 1 leaked cluster.

I wrote my own tool and it does not find any error. Both files attached,
as well as debug output from my program.

Both files are about 4G in size after unpacking. Unpack with `tar -S` to
handle sparse files.

And also, I know, that QED is deprecated, but anyway, seems qemu-img has
bug.