File upload inside list fails prior to save

Similar to #773, I found that with a file upload inside a list, the list item needs to be saved first before the file can be uploaded.

Start by reviewing issue #773 and reproducing a file upload inside a list before the list item is saved. Trace the admin list and upload entry points to identify why saving is required; done means uploads work before the item is saved, without breaking the existing list workflow.

Written by the indexing model from the issue text.