Avoid free if not seckey subkey wasn't allocated

dist/src/lib/validate.c

@@ -231,7 +231,8 @@ static void validate_key_cb_free (validate_key_cb_t *vdata){
         pgp_pubkey_free(&vdata->subkey.pubkey);
     } else if (vdata->type == PGP_PTAG_CT_SECRET_KEY) {
         pgp_seckey_free(&vdata->key.seckey);
-        pgp_seckey_free(&vdata->subkey.seckey);
+        if(vdata->subkey.seckey.pubkey.alg)
+            pgp_seckey_free(&vdata->subkey.seckey);
     }
     memset(&vdata->key, 0, sizeof(vdata->key));
     memset(&vdata->subkey, 0, sizeof(vdata->subkey));