Search Rooms: Events shown as `undefined` and some events missing in availability view

[JPromi]

Steps to reproduce

1. Go to Calendar
2. Create/Edit event
3. Go to "View all rooms (Alle Räume anzeigen)"
4. Check the availability of a room (Verfügbarkeit des Raums prüfen)

Expected behavior

• See all events that booked this room
• Show title of booked event

Actual behavior

• Not all events that booked this room are visible
• Instead of the event title, it shows undefined

App version

0.11.0

Additional info

No response