message: fix cashlib decodebase64 error return
diff: @@ -717,9 +717,9 @@ extern "C" JNIEXPORT jbyteArray JNICALL Java_bitcoinunlimited_libbitcoincash_Cod
  jstring jdata)
  {
  std::string data = toString(env, jdata);
  - bool valid = false;
  - auto dataBytes = DecodeBase64(data.c_str(), &valid);
  - if (!valid)
  + bool invalid = true;
  + auto dataBytes = DecodeBase64(data.c_str(), &invalid);
  + if (invalid)
  {
  triggerJavaIllegalStateException(env, "bad encoding");
  return jbyteArray();
  