fix for SQLite3Result::fetchArray() on setup

This PR fix the "The SQLite3Result object has not been correctly initialised" on the setup.
When the given user at the setup is added to the admin group, this also trigger the hook "post_addToGroup" on lib/public/share.php.
The query runs into an exception like this log entry:
{"app":"PHP","message":"SQLite3Result::fetchArray(): The SQLite3Result object has not been correctly initialised at \/Users\/fp\/PhpstormProjects\/ownCloud\/files_encryption\/lib\/MDB2\/Driver\/sqlite3.php#942"......