fix mime worker

app/workers/bitstream_mime_worker.rb

@@ -4,13 +4,14 @@ class BitstreamMimeWorker
   def perform(id)
     attachment = LearningObject::Attachment.find(id)
     client = DspaceService.create_client
+    return false if attachment.nil? || client.nil?
 
+    file = client.bitstreams.retrieve(id: attachment.id_dspace).open
     begin
-      file = client.bitstreams.retrieve(id: attachment.id_dspace).open
       mime = MimeMagic.by_magic(file)
       attachment.update(format: mime.mediatype, mime_type: mime.type) unless mime.blank?
     ensure
-      file.close unless file.nil?
+      file.unlink
     end
   end
 end