Fix access to property of FileInstance set to None

* soft-deleted files will have ObjectVersions that don't have an
  associated FileInstance

invenio_utilities_tuw/cli/files.py

@@ -49,7 +49,10 @@ def get_orphaned_files(location):
     # filter out those files that invenio has knowledge about
     for bucket in location.buckets:
         for obj in bucket.objects:
-            all_files.remove(obj.file.uri)
+            if obj.file:
+                # an object_version without attached file_instance
+                # likely denotes a soft-deleted file
+                all_files.remove(obj.file.uri)
 
     return all_files