Ensure a @TopicID is returned from GetTopicID()

The `GetTopicID()` function returns the `@TopicID` corresponding to a given `@TopicKey`. The only problem? If it isn't able to find the `@TopicID` then it doesn't return a value—which causes downstream implementors to falter when trying to consumer the output. To mitigate that, we're now returning a default of `-1`.

Author: JeremyCaney

OnTopic.Data.Sql.Database/Functions/GetTopicID.sql

@@ -19,6 +19,7 @@ BEGIN
   -- DECLARE AND DEFINE VARIABLES
   ------------------------------------------------------------------------------------------------------------------------------
   DECLARE	@TopicID		INT
+  SET	@TopicID		= -1
 
   ------------------------------------------------------------------------------------------------------------------------------
   -- GET TOPIC ID BASED ON TOPIC KEY