In wh_Server_KeystoreReadKey, the SHE master ECU key fallback path
(when the key is not found in cache or NVM) correctly zeroed outMeta
but then wrote len and id to the local stack variable `meta` instead
of the caller's output parameter `outMeta`. This left the caller with
a zeroed metadata struct (len=0, id=0), contradicting the intended
behavior of returning WH_SHE_KEY_SZ and the correct keyId.

Also fix two related issues in the same function:
 - Use sizeof(*outMeta) instead of sizeof(meta) in memset/memcpy
   calls targeting outMeta, for clarity and consistency with the
   target variable.
 - Add a NULL check on `out` before memset in the SHE fallback,
   matching the guards already present in the cache and NVM paths.

Add a direct server-side test that exercises the fallback by reading
the master ECU key without provisioning it, verifying the returned
metadata contains the correct len and id.

Signed-off-by: Sameeh Jubran <sameeh@wolfssl.com>