fix too many players bug

server/src/instance.rs

@@ -155,6 +155,10 @@ impl Instance {
     }
 
     fn add_player(&mut self, player: Player) -> Result<&mut Instance, Error> {
+        if self.players.len() >= self.max_players {
+            return Err(err_msg("game full"))
+        }
+
         match self.players.iter().find(|p| p.id == player.id) {
             Some(_p) => return Err(err_msg("already joined")),
             None => (),