message: additional callback check method
diff: @@ -34,6 +34,14 @@ public class SovrinJava {
  return true;
  }
  + protected static boolean checkCallback(CompletableFuture<? extends SovrinJava.Result> future, int err) {
  +
  + ErrorCode errorCode = ErrorCode.valueOf(err);
  + if (! ErrorCode.Success.equals(errorCode)) { future.completeExceptionally(SovrinException.fromErrorCode(errorCode, err)); return false; }
  +
  + return true;
  + }
  +
  protected static void checkResult(int result) throws SovrinException {
  ErrorCode errorCode = ErrorCode.valueOf(result);
  