sandbox: Double free when initializing the HSv3 config
In `main.c`:
```
/* steals references */
sandbox_cfg_allow_open_filename(&cfg, file_name);
sandbox_cfg_allow_open_filename(&cfg, tmp_name);
tor_free(file_name);
```
... freeing after stealing a reference is really not good :).
Introduced in 5d2506d70cd which was never released.
issue