Expiration time goes into incorrect state after first upload #354

To reproduce:

1. Go to upload page
2. Change the expiration time to 1 year
3. Upload a file
4. Click "Upload another"

Expected: On "Upload another" screen, expiration time is either the default (1 month) or the most recently selected option (1 year)

Actual: Expiration time shows as "Custom" with no specified date. If you upload, it treats the expiration time as one month.