avoid negative value

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@16360 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/model/PeriodicWork.java

@@ -80,7 +80,7 @@ public abstract class PeriodicWork extends SafeTimerTask implements ExtensionPoi
      * By default it chooses the value randomly between 0 and {@link #getRecurrencePeriod()}
      */
     public long getInitialDelay() {
-        return new Random().nextLong()%getRecurrencePeriod();
+        return Math.abs(new Random().nextLong())%getRecurrencePeriod();
     }
 
     /**