Subscription totals now show "Unavailable" instead of an incomplete number

On a single subscription's admin page, the next-order total and the invoice's subtotal and total are built using any upcoming edits on that order. When the read for those upcoming edits failed, the page still showed a total, but one that silently left out whatever the pending edits would have added.

Those totals now show "Unavailable" instead once that read has failed, so you're not shown a number that looks complete but isn't. The label stays through any retry until it succeeds and the real total can be shown. Shipping price is unaffected, since it doesn't depend on upcoming edits.