Changing file in edit view can lose data

[thenewguy]

We need to protect file deletion with transaction.on_commit so that we do not delete the old file on disk and then find out we can't save - this leaves us in a bad spot:

wagtailmedia/wagtailmedia/views/media.py

Line 146 in 47cb76f

original_file.storage.delete(original_file.name)