function _onCheckIssue(){
            var waChecked = $(htVar.sIssueCheckedBoxesSelector);
            var bDisabled = (waChecked.length === 0);

            htElement.welMassUpdateButtons.attr('disabled', bDisabled);

            if(bDisabled){
                _restoreLabelList();
            } else {
                _makeLabelListByChecked(waChecked);
            }
        }
When check an issue, enable Mass Update dropdowns if only one or
more issues are checked, otherwise disable them.