Fix minor issue in LongTask API

modules/LongTaskAPI/src/main/java/org/gephi/utils/longtask/api/LongTaskExecutor.java

@@ -41,10 +41,10 @@
  */
 package org.gephi.utils.longtask.api;
 
+import java.util.List;
 import java.util.Timer;
 import java.util.TimerTask;
 import java.util.concurrent.Future;
-import java.util.concurrent.FutureTask;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.ThreadPoolExecutor;
@@ -328,11 +328,16 @@ public final class LongTaskExecutor {
                 if (task.future != null) {
                     task.future.cancel(interruptCancel);
                 }
+                cancelTimer.cancel();
                 cancelTimer = null;
                 if (task.progress != null) {
                     task.progress.finish();
                 }
                 finished(task);
+
+                if (!inBackground) {
+                    Thread.currentThread().interrupt();
+                }
             }
         }
     }