ensure consumed offset doesn't go past end of topic... this was causing an offset out of range error.

src/KafkaNET.Library/ZooKeeperIntegration/Listeners/ZKRebalancerListener.cs

@@ -514,7 +514,7 @@ namespace Kafka.Client.ZooKeeperIntegration.Listeners
                 leader,
                 partitionId,
                 queue,
-                offset,
+                offset - 1,
                 offset,
                 offset,
                 this.config.FetchSize,