Fix fail to call lambda without arguments.

refs SkygearIO#276

This bug occurs after adding auto upload asset when calling lambda, sdk will check the arguments if there is any not updated assets.
Update the callLambdaFunction implementation to skip the presave.

skygear/src/main/java/io/skygear/skygear/Container.java

@@ -203,7 +203,9 @@ public void sendRequest(Request request) {
      * @param handler the response handler
      */
     public void callLambdaFunction(String name, LambdaResponseHandler handler) {
-        this.callLambdaFunction(name, (Object[]) null, handler);
+        LambdaRequest request = new LambdaRequest(name, (Object)null);
+        request.responseHandler = handler;
+        this.requestManager.sendRequest(request);
     }
 
     /**