SyncJournalDb: Fix warnings

I got those warnings for the latter sync runs:
11-19 10:58:15:997 QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.
11-19 10:58:15:997 QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.