Ensure prefix_options are set on assets returned from Asset.find. Fixes #14

lib/shopify_api/resources/asset.rb

@@ -55,7 +55,9 @@ module ShopifyAPI
         params = {:asset => {:key => args[0]}}
         params = params.merge(args[1][:params]) if args[1] && args[1][:params]
         path_prefix = params[:theme_id] ? "/admin/themes/#{params[:theme_id]}" : "/admin"
-        find(:one, :from => "#{path_prefix}/assets.#{format.extension}", :params => params)
+        resource = find(:one, :from => "#{path_prefix}/assets.#{format.extension}", :params => params)
+        resource.prefix_options[:theme_id] = params[:theme_id] if resource && params[:theme_id]
+        resource
       end
     end