NCBC-581: System.InvalidOperationException when server list is empty

Change-Id: I8fdef46b4057bc9f3b898b789fcccd78f689fdb6
Reviewed-on: http://review.couchbase.org/40546
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Brett Lawson <brett19@gmail.com>