Let the asso pigliatutto ace capture itself on a bare table

With the rule enabled, an ace played on an empty table goes straight to
the player's capture pile instead of staying on the table: it counts as
the last capture but never scores a scopa. An empty capture request now
matches only that self-capture option, so requesting nothing still can't
satisfy a real capture.

server/README.md

@@ -272,9 +272,10 @@ must dismiss. A play attempted in this phase is rejected with an
   instantly, regardless of the score.
 - Optional *asso pigliatutto* rule (per-game `asso_pigliatutto` creation
   option, default off): an ace played when no equal rank is on the table
-  sweeps every card on the table. The sweep never scores a scopa, and the
-  mandatory equal-rank capture still applies when another ace is on the
-  table.
+  sweeps every card on the table — or captures itself when the table is
+  empty. The capture never scores a scopa, but it counts as the last
+  capture, and the mandatory equal-rank capture still applies when another
+  ace is on the table.
 - The match ends when a team reaches the target score (default 11,
   configurable per game via the `target_score` creation option) with a
   clear lead; a tie at or above the target is broken by another hand.