Fix crash in attachment handling when we close on error

system/rest/attachment.go

@@ -118,13 +118,13 @@ func (ctrl Attachment) serve(ctx context.Context, attachmentID uint64, preview,
 			fh, err = ctrl.attachment.OpenOriginal(att)
 		}
 
-		defer fh.Close()
-
 		if err != nil {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return
 		}
 
+		defer fh.Close()
+
 		name := url.QueryEscape(att.Name)
 
 		if download {