Prevent a spectator race condition in arcade games

Previously, a player would erratically become a spectator if s/he
spammed the "spectate next player" action between rounds (i.e.
left-click while spectating a player).

Plugins/Nautilus.Game.Arcade/src/nautilus/game/arcade/managers/GameSpectatorManager.java

@@ -224,6 +224,9 @@ public class GameSpectatorManager implements Listener
 			@Override
 			public void run()
 			{
+				if (Manager.GetGame().IsAlive(player))
+					return;
+
 				Player ptarget = null;
 				if (target instanceof Player)
 					ptarget = (Player) target;