Fix ONC logic error

A bug in onc_translator_onc_to_shill.cc is triggering a DCHECK when
a property is set in a previously non-existent dictionary.

This is a trivial fix to code that is subtle but clearly incorrect
by inspection.

BUG=none

Review URL: https://codereview.chromium.org/838043003

Cr-Commit-Position: refs/heads/master@{#311357}

chromeos/network/onc/onc_translator_onc_to_shill.cc

@@ -353,9 +353,10 @@ void TranslateONCHierarchy(const OncValueSignature& signature,
     base::DictionaryValue* nested_shill_dict = NULL;
     target_shill_dictionary->GetDictionaryWithoutPathExpansion(
         *it, &nested_shill_dict);
-    if (!nested_shill_dict)
+    if (!nested_shill_dict) {
       nested_shill_dict = new base::DictionaryValue;
-    target_shill_dictionary->SetWithoutPathExpansion(*it, nested_shill_dict);
+      target_shill_dictionary->SetWithoutPathExpansion(*it, nested_shill_dict);
+    }
     target_shill_dictionary = nested_shill_dict;
   }
   // Translates fields of |onc_object| and writes them to