Fixed a potential concurrency bug

astrid/plugin-src/com/todoroo/astrid/actfm/sync/ActFmSyncThread.java

@@ -240,10 +240,12 @@ public class ActFmSyncThread {
     };
 
     private void incrementProgress() {
+        synchronized (progressBarLock) {
             if (activity != null) {
                 activity.runOnUiThread(incrementProgressRunnable);
             }
         }
+    }
 
     public synchronized void setTimeForBackgroundSync(boolean isTimeForBackgroundSync) {
         this.isTimeForBackgroundSync = isTimeForBackgroundSync;