temporary fix for vending items not saving correct cart ID > prompt player to relog if we have a new item in cart

src/map/pc.c

@@ -4604,6 +4604,9 @@ int pc_cart_additem(struct map_session_data *sd,struct item *item_data,int amoun
 	if( (w = data->weight*amount) + sd->cart_weight > sd->cart_weight_max )
 		return 1;
 
+	//id no longer points to inventory/kafra id, while we get a new one, we don't want to mess up vending creation
+	item_data->id = 0;
+
 	i = MAX_CART;
 	if( itemdb_isstackable2(data) && !item_data->expire_time )
 	{

src/map/vending.c

@@ -345,6 +345,14 @@ bool vending_openvending(struct map_session_data* sd, const char* message, const
 		sd->vending[i].amount = amount;
 		sd->vending[i].value = min(value, (unsigned int)battle_config.vending_max_value);
 
+		//player just moved item to cart and we don't have the correct cart ID yet
+		if (sd->status.cart[sd->vending[i].index].id == 0) {
+			snprintf(msg, 256, "Item %s is not yet saved. Please re-log in order to correctly save your vending.", idb->jname);
+			clif_displaymessage(sd->fd, msg);
+			clif_skill_fail(sd, MC_VENDING, USESKILL_FAIL_LEVEL, 0);
+			return false;
+		}
+
 		i++; // item successfully added
 	}