prevent Self-suppression not permitted

Author: zhongkechen

sdk/src/main/java/software/amazon/lambda/durable/operation/ParallelOperation.java

@@ -113,6 +113,9 @@ public ParallelResult get() {
     /** Calls {@link #get()} if not already called. Guarantees that the context is closed. */
     @Override
     public void close() {
+        if (isJoined.get()) {
+            return;
+        }
         join();
     }