Don't allow inactive sync providers (like gtasks) to sync in background

api/src/com/todoroo/astrid/sync/SyncV2BackgroundService.java

@@ -77,7 +77,9 @@ abstract public class SyncV2BackgroundService extends Service {
         if(!getSyncUtilities().isLoggedIn())
             return;
 
-        getSyncProvider().synchronizeActiveTasks(false, new SyncResultCallbackAdapter() {
+        SyncV2Provider provider = getSyncProvider();
+        if (provider.isActive())
+            provider.synchronizeActiveTasks(false, new SyncResultCallbackAdapter() {
                 @Override
                 public void finished() {
                     getSyncUtilities().recordSuccessfulSync();