We sometimes do things like `memset(&cert, 0, sizeof(cert))` then
`copy_Certificate(&cert, &cert_copy)`, and then we end up leaking a
byte in `der_copy_octet_string()` due to it having this code:
```C
der_copy_octet_string (const heim_octet_string *from, heim_octet_string *to)
{
assert(from->length == 0 || (from->length > 0 && from->data != NULL));
if (from->length == 0)
to->data = calloc(1, 1);
else
to->data = malloc(from->length);
...
}
```
The traces where this happens always involve the `_save` field of
`Name` or `TBSCertificate`.
This code was assuming that length 0 octet strings are expected to have
a non-NULL `data`, probably in case the C library's allocator returns
non-NULL pointers for `malloc(0)`, but then, why not just call
`malloc(0)`? But calling `malloc(0)` would then still lead to this leak
in on such systems.
Now, `der_free_octet_string()` does unconditionally `free()` the
string's `data`, so the leak really is not there but elsewhere, probably
in `lib/asn1/template.c:_asn1_free()`, but it clearly does
`der_free_octet_string()` the `_save` field of types that have it.
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