vrfs-492: added check for pre-existing MSUH record in self.save

ruby/lib/jam_ruby/models/music_session_user_history.rb

@@ -24,7 +24,10 @@ module JamRuby
     end
 
     def self.save(music_session_id, user_id, client_id)
-      session_user_history = MusicSessionUserHistory.new()
+      return true if 0 < self.where(:music_session_id => music_session_id, 
+                                    :user_id => user_id, 
+                                    :client_id => client_id).count
+      session_user_history = MusicSessionUserHistory.new
       session_user_history.music_session_id = music_session_id
       session_user_history.user_id = user_id
       session_user_history.client_id = client_id