All other users of derive_simple_privkey(...) check the return value:
```
channeld/channel.c: if (!derive_simple_privkey(&peer->our_secrets.htlc_basepoint_secret,
lightningd/test/run-commit_tx.c: if (!derive_simple_privkey(&x_remote_htlc_basepoint_secret,
lightningd/test/run-commit_tx.c: if (!derive_simple_privkey(&x_local_delayed_payment_basepoint_secret,
lightningd/test/run-commit_tx.c: if (!derive_simple_privkey(&x_local_htlc_basepoint_secret,
lightningd/test/run-key_derive.c: if (!derive_simple_privkey(&base_secret, &base_point,
onchaind/onchain.c: if (!derive_simple_privkey(&secrets->delayed_payment_basepoint_secret,
onchaind/onchain.c: if (!derive_simple_privkey(&secrets->payment_basepoint_secret,
onchaind/onchain.c: if (!derive_simple_privkey(&secrets->htlc_basepoint_secret,
onchaind/onchain.c: if (!derive_simple_privkey(&secrets->payment_basepoint_secret,
onchaind/onchain.c: if (!derive_simple_privkey(&secrets->htlc_basepoint_secret,
```