Fix nil error regression from #9229 in tootctl media remove (#9239)

Fix #9237

lib/mastodon/media_cli.rb

@@ -53,7 +53,7 @@ module Mastodon
             Maintenance::UncacheMediaWorker.new.perform(m) unless options[:dry_run]
             options[:verbose] ? say(m.id) : say('.', :green, false)
             processed += 1
-            size      += m.file_file_size
+            size      += m.file_file_size || 0
           end
         end
       end