memzero() the state if we call generichash_final() twice

src/libsodium/crypto_generichash/blake2b/ref/blake2b-ref.c

@@ -359,6 +359,7 @@ blake2b_final(blake2b_state *S, uint8_t *out, uint8_t outlen)
         sodium_misuse("blake2b_final(): unsupported output length");
     }
     if (blake2b_is_lastblock(S)) {
+        sodium_memzero(S, sizeof *S);
         return -1;
     }
     if (S->buflen > BLAKE2B_BLOCKBYTES) {