[BUGFIX] missing parameter for implode

Use the preferred syntax for implode()

Change-Id: Id5db3a209903978979eba971f7f53180a850289a
Releases: 6.0, 4.7, 4.6, 4.5
Fixes: #34695
Reviewed-on: http://review.typo3.org/10192
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert