[BUGFIX] Invalid toolbar markup with TYPO3 6.x

Thanks to Eric Chavaillaz for spotting this.

Change-Id: I416fb2a2f1e0009e2137c719949c7e546cea3977
Fixes: #55358
Reviewed-on: https://review.typo3.org/27070
Reviewed-by: Eric Chavaillaz
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers