ResourceNotFoundException: EntityRepresentationModel not found!

Rooms that don't have a map image (yet), create resourceNotFoundExceptions (we are at several thousands exceptions and counting in Sentry...). We don't expect every room to have a map, so this should just be a 404 and no exception.

Sentry Issue: QUEUE-9P

ResourceNotFoundException: EntityRepresentationModel not found!
    at nl.tudelft.queue.controller.RoomController.getRoomImageFile(RoomController.java:45)
    at nl.tudelft.queue.controller.RoomController$$FastClassBySpringCGLIB$$d3d95306.invoke(<generated>)
    at nl.tudelft.queue.controller.RoomController$$EnhancerBySpringCGLIB$$2780f9b9.getRoomImageFile(<generated>)
...
(120 additional frame(s) were not displayed)

A Request (/room/map/230) raised an exception