[FOLLOWUP][BUGFIX] Remove space between buttons in button-group

Prevent overlapping of buttons in irre-header.

Releases: master
Resolves: #65110
Change-Id: I96f5b384dc91d0c38c253f5fc2e397f12482d0c4
Reviewed-on: http://review.typo3.org/37054


Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Tested-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>