PHP Warning: implode(): Invalid arguments passed

Summary:
A first attempt to fix the following warning:

PHP Warning:  implode(): Invalid arguments passed in /usr/share/kolab-syncroton/lib/kolab_sync_data.php on line 752

Test Plan: None

Reviewers: machniak

Reviewed By: machniak

Subscribers: machniak

Differential Revision: https://git.kolab.org/D455