fix 'still reachable' memory leaks

Valgrind reports nearly 8MB of `still reachable` leaks from the compressible and incompressible test cases:
compressible

```
 ==22758==    still reachable: 7,984,809 bytes in 431 blocks
```

incompressible

```
 ==21837==    still reachable: 7,692,212 bytes in 320 blocks
```
