CBQE-2304 fix error when no log collected

Change-Id: I122513bc7104eda33a3cf87a46832384a5c00210
Reviewed-on: http://review.couchbase.org/39195
Reviewed-by: Thuan Nguyen <soccon@gmail.com>
Tested-by: Thuan Nguyen <soccon@gmail.com>