Title: Fixed wrong JSON format when using stats queries together with header columns
Level: 1
Component: livestatus
Compatible: compat
Version: 1.2.7i3
Date: 1438069896
Class: fix

e.g. this query lead to invalid JSON output:

GET statehist
Filter: time >= 1425168000
Filter: time < 1427846400
Filter: host_name = name
Filter: service_description = Description
Stats: sum duration_part_ok
OutputFormat: json
ColumnHeaders: on 

Output:
[["stats_1"][0.0000000000e+00]]

