Replaced returnVal with topic.Id

As part of #9b5d01e, we assigned the `GetReturnCode()` directly to `topic.Id`. But we kept the (now) unused `returnVal`. This introduced a potential error, as the `Save()` procedure returns the `returnVal`. To fix this, the `returnVal` has now been removed, and `Save()` instead returns the `topic.Id`.

Author: JeremyCaney

OnTopic.Data.Sql/SqlTopicRepository.cs

@@ -727,7 +727,6 @@ public override int Save([NotNull]Topic topic, bool isRecursive = false, bool is
       \-----------------------------------------------------------------------------------------------------------------------*/
       var connection            = new SqlConnection(_connectionString);
       var command               = (SqlCommand?)null;
-      var returnVal             = -1;
 
       try {
 
@@ -825,7 +824,7 @@ public override int Save([NotNull]Topic topic, bool isRecursive = false, bool is
       /*------------------------------------------------------------------------------------------------------------------------
       | Return value
       \-----------------------------------------------------------------------------------------------------------------------*/
-      return returnVal;
+      return topic.Id;
 
     }