RSVP: 1 additional guest is counted as 2 (off-by-one overcount)

When RSVPing with "Additional guests" set to 1, the guest is counted as 2. The attendee count and the avatar overflow are inflated by one. **Expected:** Selecting 1 additional guest should count as 1 extra person (total = you + 1). **Evidence:** On an event RSVP with "Additional guests: 1" selected, the Attendees avatar overflow shows "+2" for that single +1 guest, and the going total is higher than the actual number of people. **Where:** Event RSVP — "Additional guests" selector and the Attendees count / avatar overflow. **Steps to reproduce:** 1. Open an event and RSVP "Going" 2. Set "Additional guests" to 1 3. View the Attendees section — the guest is reflected as +2 instead of +1, and the going count is one too high