fix: skip travels whose hotel is missing from the master data

generateFilesMap() read ->name straight off $hotels[$hotelId] with no
guard, so a travel referencing a hotel absent from hotel.xml produced an
undefined-key warning and an entry with a null label -- a hotel in
/api/travels that resolves nowhere. No row hits this in the current
snapshot, which is why it has never surfaced.

Co-Authored-By: Claude Opus 5 <[email protected]>

src/BusProNet/XmlLoader/TravelLoader.php

@@ -92,6 +92,13 @@ class TravelLoader extends AbstractLoader
                             ->each(function (Crawler $hotelNode) use (&$mapping, $hotels, $travelId) {
                                 $hotelId = (int) $hotelNode->attr('idbuspro');
 
+                                // A travel may reference a hotel that hotel.xml does not carry.
+                                // Reading ->name off the miss would fatal the whole mapping, not
+                                // just this entry, and take /api/travels down with it.
+                                if (false === isset($hotels[$hotelId])) {
+                                    return;
+                                }
+
                                 $mapping[$travelId]['hotels'][$hotelId] = [
                                     'id' => $hotelId,
                                     'code' => $hotelNode->attr('code'),