Don't start an announcer task if there are no scripts

src/main/java/io/github/dre2n/dungeonsxl/DungeonsXL.java

@@ -606,8 +606,10 @@ public class DungeonsXL extends BRPlugin {
      * start a new AnnouncerTask
      */
     public void startAnnouncerTask(long period) {
+        if (!announcers.getAnnouncers().isEmpty()) {
             announcerTask = new AnnouncerTask(announcers).runTaskTimer(this, 0L, period);
         }
+    }
 
     /**
      * @return the AnnouncerTask