uploads: show similar images for disk uploads.

Fix the upload page so that it shows similar images (IQDB matches) for
files uploaded from your computer. Before this only worked for files
uploaded from a source.

app/models/upload.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class Upload < ApplicationRecord
+  extend Memoist
+
   MAX_VIDEO_DURATION = 140
 
   attr_accessor :file
@@ -76,7 +78,14 @@ class Upload < ApplicationRecord
     raise
   end
 
+  def source_strategy
+    return nil if source.blank?
+    Sources::Strategies.find(source, referer_url)
+  end
+
   def self.available_includes
     [:uploader, :upload_media_assets, :media_assets]
   end
+
+  memoize :source_strategy
 end