mojo: Fix c++ bindings so serialization of empty arrays doesn't crash.

mojo/public/cpp/bindings/lib/array_serialization.h

Index: mojo/public/cpp/bindings/lib/array_serialization.h
diff --git a/mojo/public/cpp/bindings/lib/array_serialization.h b/mojo/public/cpp/bindings/lib/array_serialization.h
index e73553d89b39a6f2ba4142cd6e83ffec769a3acb..eacf298ec80ea46fffebe0afa499a32f83325316 100644
--- a/mojo/public/cpp/bindings/lib/array_serialization.h
+++ b/mojo/public/cpp/bindings/lib/array_serialization.h
@@ -63,11 +63,13 @@ struct ArraySerializer<E, F, false> {
     static_assert((IsSame<ElementValidateParams, NoValidateParams>::value),
                   "Primitive type should not have array validate params");
 
-    memcpy(output->storage(), &input.storage()[0], input.size() * sizeof(E));
+    if (input.size())
+      memcpy(output->storage(), &input.storage()[0], input.size() * sizeof(E));
   }
   static void DeserializeElements(Array_Data<F>* input, Array<E>* output) {
     std::vector<E> result(input->size());
-    memcpy(&result[0], input->storage(), input->size() * sizeof(E));
+    if (input->size())
+      memcpy(&result[0], input->storage(), input->size() * sizeof(E));
     output->Swap(&result);
   }
 };