avoid NPE if trying to stop tracking for a TracTrac race that hasn't been found

Change-Id: Ifa266cc5decd6f1bfa6287c6a87ed0df48baa515

java/com.sap.sailing.domain.tractracadapter/src/com/sap/sailing/domain/tractracadapter/impl/TracTracRaceTrackerImpl.java

@@ -662,7 +662,9 @@ public class TracTracRaceTrackerImpl extends AbstractRaceTrackerImpl
     @Override
     public void raceNotLoaded(String reason) throws MalformedURLException, IOException, InterruptedException {
         logger.severe("Race for tracker "+this+" with ID "+getID()+" did not load: "+reason+". Stopping tracker.");
-        trackedRegattaRegistry.stopTracking(regatta, race);
+        if (race != null) {
+            trackedRegattaRegistry.stopTracking(regatta, race);
+        }
     }
 
     @Override