Use GTFS ID when vehicle license plate is not available

 lib/mapper.php

@@ -135,8 +135,8 @@
                $num = $gtfsTrip['num'];
                if(!is_array($data) || !isset($data['num'])) {
                    $data = [
                        'num' => $num ?: '',
                        'low' => 2,
                        'num' => $num ?: $gtfsTrip['id'],
                        'low' => NULL,
                    ];
                } elseif($data['num'] != $num) {
                    // Ignore due to incorrect depot markings in the data