Deck pages open again when the export has expired

Opening a deck whose PowerPoint export had expired on our provider's side could leave the page stuck on its loading skeleton indefinitely, and the download button on those decks could spin without ever answering. The check that asks whether the file is still there was waiting on a cleanup step that never finished. It no longer waits: the page opens in about a second and tells you plainly that the export has expired, and the download answers straight away instead of hanging. Every request in that check now has a time limit as well, so a slow storage host can delay the file-size line but can no longer hold the page.