add try-finally

src/main/java/com/github/nkzawa/thread/EventThread.java

@@ -70,9 +70,13 @@ public class EventThread extends Thread {
         getExecutorService().execute(new Runnable() {
             @Override
             public void run() {
+                try {
                     task.run();
+                } finally {
                     if (counter.decrementAndGet() == 0) {
                         service.shutdown();
+                        thread = null;
+                    }
                 }
             }
         });