Bug 725597 - SafeBrowsing fails to update persistent PrefixSet on Windows. r=dcamp

toolkit/components/url-classifier/Classifier.cpp

@@ -587,7 +587,8 @@ Classifier::ApplyTableUpdates(nsTArray<TableUpdate*>* aUpdates,
 #if defined(DEBUG) && defined(PR_LOGGING)
   prefixSet->Dump();
 #endif
-  prefixSet->WriteFile();
+  rv = prefixSet->WriteFile();
+  NS_ENSURE_SUCCESS(rv, rv);
 
   // This will drop all the temporary storage used during the update.
   rv = store->FinishUpdate();