[BUGFIX] Report not shown in IE 7 and 8 when CheckLink tab is hidden

With showCheckLinkTab = 0 linkvalidator does not load in IE 7 and 8
since trailing commas in array literals are not ignored. This leads to a
JavaScript error in ExtJS.

Solution: Output comma only when the CheckLink tab is added.

Resolves: #36515
Releases: 4.7, 6.0, 6.1
Change-Id: I8e6441f48664da2bd400c4e9b14179f6f520320f
Reviewed-on: https://review.typo3.org/18953
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe