message: Delete stmt_ref if preparing had no success
diff: @@ -275,7 +275,13 @@ JNIEXPORT jobject JNICALL Java_org_duckdb_DuckDBNative_duckdb_1jdbc_1prepare(JNI
  if (!stmt_ref->stmt->success) {
  string error_msg = string(stmt_ref->stmt->error);
  stmt_ref->stmt = nullptr;
  +
  + // No success, so it must be deleted
  + delete stmt_ref;
  env->ThrowNew(J_SQLException, error_msg.c_str());
  +
  + // Just return control flow back to JVM, as an Exception is pending anyway
  + return 0;
  }
  return env->NewDirectByteBuffer(stmt_ref, 0);
  }
  