Using remote_video media type causes an error because there is no "file"

[wgilling]

When the remote_video media type is used on an item, the code throws an error when trying to call the getSourceFile() method.

This occurs on an item that is using a media type of "remote_video" when navigating to the item's media page such as http://localhost:8000/node/351/media.

The call stack for this error
Error: Call to undefined method Drupal\Core\Field\FieldItemList::referencedEntities() in Drupal\islandora\MediaSource\MediaSourceService->getSourceFile() (line 130 of /var/www/html/drupal/web/modules/contrib/islandora/src/MediaSource/MediaSourceService.php)
#0 /var/www/html/drupal/web/modules/contrib/islandora_riprap/src/Riprap/IslandoraRiprapUtils.php(74): Drupal\islandora\MediaSource\MediaSourceService->getSourceFile(Object(Drupal\media\Entity\Media))
#1 /var/www/html/drupal/web/modules/contrib/islandora_riprap/src/Plugin/views/field/RiprapResults.php(43): Drupal\islandora_riprap\Riprap\IslandoraRiprapUtils->getFedoraUrl('17')
#2 /var/www/html/drupal/web/core/modules/views/src/Plugin/views/field/FieldPluginBase.php(1156): Drupal\islandora_riprap\Plugin\views\field\RiprapResults->render(Object(Drupal\views\ResultRow))

This does not happen unless the remote_video media type is being used. To set this up, as admin navigate to "Add media type": http://localhost:8000/admin/structure/media/add -- NOTE: this media type will also need to have the two fields as are configured for all other islandora media types - these are "media_use" (a taxonomy entity reference) and "media_of" (entity reference) in order to be able to have media of this type show up in the media view without throwing another error.