media assets: add script to fix assets with deleted files.

Mark assets that have missing files as expunged. This happened with
uploads that were abandoned and had their files deleted, but that didn't
destroy their media asset record.

Fixes an issue where uploads could have missing files because someone
resumed an abandoned upload that had its files deleted.

script/fixes/082_fix_expunged_media_assets.rb

@@ -0,0 +1,12 @@
+#!/usr/bin/env ruby
+
+require_relative "../../config/environment"
+
+assets = MediaAsset.active
+
+assets.parallel_each do |asset|
+  asset.variant(:original).open_file
+rescue
+  puts "id=#{asset.id} md5=#{asset.md5} file_ext=#{asset.file_ext} status=expunged"
+  asset.update!(status: :expunged)
+end