added missing write locking for CrossTrackErrorSumAndNumberOfFixesTrack.add

Change-Id: Ic3c42de5116b28d18ac22073f344c82d5bc8d546

java/com.sap.sailing.domain/src/com/sap/sailing/domain/tracking/impl/CrossTrackErrorCache.java

@@ -114,7 +114,7 @@ public class CrossTrackErrorCache extends AbstractRaceChangeListener {
         }
         
         public boolean add(CrossTrackErrorSumAndNumberOfFixes entry) {
-            return getInternalRawFixes().add(entry);
+            return super.add(entry, /* replace */ true);
         }
     }