fix for NPE in TDBatcher

TouchDB-Android/src/com/couchbase/touchdb/support/TDBatcher.java

@@ -72,7 +72,9 @@ public void queueObject(T object) {
     public void flush() {
         synchronized(this) {
             if(inbox != null) {
-                handler.removeCallbacks(processNowRunnable);
+                if (handler != null) {
+                  handler.removeCallbacks(processNowRunnable);
+                }
                 processNow();
             }
         }