Fixes #6584 (#6585)

lib/tasks/mastodon.rake

@@ -476,10 +476,12 @@ namespace :mastodon do
       time_ago = ENV.fetch('NUM_DAYS') { 7 }.to_i.days.ago
 
       MediaAttachment.where.not(remote_url: '').where.not(file_file_name: nil).where('created_at < ?', time_ago).find_each do |media|
+        if media.file.exists?
           media.file.destroy
           media.save
         end
       end
+    end
 
     desc 'Set unknown attachment type for remote-only attachments'
     task set_unknown: :environment do