Fix null pointer exception with dataSourceManager in TrackDataHub

MyTracks/src/com/google/android/apps/mytracks/content/TrackDataHub.java

@@ -117,9 +117,11 @@ public class TrackDataHub implements DataSourceListener {
     runInHanderThread(new Runnable() {
         @Override
       public void run() {
+        if (dataSourceManager != null) {
           dataSourceManager.updateListeners(trackDataManager.getRegisteredTrackDataTypes());
           loadDataForAll();
         }
+      }
     });
   }
 
@@ -173,10 +175,12 @@ public class TrackDataHub implements DataSourceListener {
     runInHanderThread(new Runnable() {
         @Override
       public void run() {
+        if (dataSourceManager != null) {
           trackDataManager.registerListener(trackDataListener, trackDataTypes);
           dataSourceManager.updateListeners(trackDataManager.getRegisteredTrackDataTypes());
           loadDataForListener(trackDataListener);
         }
+      }
     });
   }
 
@@ -189,9 +193,11 @@ public class TrackDataHub implements DataSourceListener {
     runInHanderThread(new Runnable() {
         @Override
       public void run() {
+        if (dataSourceManager != null) {
           trackDataManager.unregisterListener(trackDataListener);
           dataSourceManager.updateListeners(trackDataManager.getRegisteredTrackDataTypes());
         }
+      }
     });
   }