Fix sync_espn treating unfilled draft slots as real picks

ESPN draftDetail returns every slot in the draft order, filled or not --
a slot nobody has picked yet comes back with playerId -1 rather than
being omitted. sync_espn was recording these as picks (unmatched, since
-1 has no crosswalk entry), so a league whose draft had not even started
came back as hundreds of picks in and dozens of rounds ahead of reality.
Skip playerId -1/None entries; only real picks are returned now.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>