[inventory] don't double-link the children by appending it twice

app/controllers/inventory_objects_controller.rb

@@ -59,7 +59,7 @@ class InventoryObjectsController < ApplicationController
     if params[:file_link_id]
       # TODO: how to constrain this, it passed an untrusted boundary?
       @file_datum = FileDatum.find(params[:file_link_id])
-      @object.links_to.append(@file_datum.attach_to(@object))
+      @file_datum.attach_to(@object)
     end
 
     @file_datum = FileDatum.new unless params[:file_link_id]