Fix error message when copyMultiplayer is missing

The error is just cosmetic, functionality stayed the same.

copyThrower.gd

@@ -156,7 +156,7 @@ func _throw_hearts_in_queue(delta: float) -> void:
 		if not skeleton: return
 
 		# copyMultiplayer support: Target a random player's skeleton.
-		var copyMP = $"../copyMultiplayer"
+		var copyMP = get_node_or_null("../copyMultiplayer")
 		if copyMP: skeleton = ([ skeleton ] + copyMP.get_all_sync_controllers()
 			.map(func(c): return c.skeleton).filter(func(s): return s != null)).pick_random()