Mojo cpp bindings: More clear checks for array num_bytes and num_elements.

mojo/public/cpp/bindings/lib/string_serialization.cc

Index: mojo/public/cpp/bindings/lib/string_serialization.cc
diff --git a/mojo/public/cpp/bindings/lib/string_serialization.cc b/mojo/public/cpp/bindings/lib/string_serialization.cc
index 0044b1b9cff67a4523a60e69c2719546c18eb60c..10d09e23a91796029782dd15bf40823b8fd638c2 100644
--- a/mojo/public/cpp/bindings/lib/string_serialization.cc
+++ b/mojo/public/cpp/bindings/lib/string_serialization.cc
@@ -19,7 +19,8 @@ void Serialize_(const String& input, internal::Buffer* buf,
   if (input) {
     internal::String_Data* result =
         internal::String_Data::New(input.size(), buf);
-    memcpy(result->storage(), input.data(), input.size());
+    if (result)
+      memcpy(result->storage(), input.data(), input.size());
     *output = result;
   } else {
     *output = NULL;