v0.22.1 — Live frame when there is no snapshot

• live_hires_fallback now also covers the case its name promises: no snapshot at all.
  It said "on a failed snapshot, ask go2rtc for a full frame", but only handled one of the
  two ways a snapshot can fail — one that exists and holds no face. When Frigate produced
  no snapshot, FaceID did nothing: the event never entered the queue (no has_snapshot),
  so even live_hires_mode: always never ran. Reported in #14.
• This matters for setups with snapshots.required_zones, where Frigate withholds the
  snapshot while the person stands plainly in the picture. It could not surface here —
  our Frigate has no required_zones, and no snapshot from Frigate appears zero times
  in 14 days of logs.
• A recognition from a frame fetched without a snapshot binds nothing to the event: no
  sub_label, no best_score. Without the snapshot nothing says who the event is about,
  which is the same reason live_hires_mode: always already behaved that way. It still
  counts toward presence and fires faceid/event.
• The poll path still requires a snapshot on purpose: it picks up stragglers up to five
  minutes old, and a frame from now no longer shows that person.