Batch export is not working correctly

Updated patch. I found an issue where in exported XML file last close tag was missed.

@andriic thank you very much for your work on this!

Can we please split this into two tickets? Let's use this ticket to fix the offset issue, and open a new ticket to deal with the queue issue(s). I will need some additional info on how to reproduce the last two issues from the ticket description:

- not correct condition to check how many items in queue. It will not work if you have a couple of exports.
- queue api will not work correct if there are more than 1 batch export exists.

I have a site using multiple batch exports and it seems to work correctly for me, so interested in how to reproduce. Thanks!

Hi @smulvih2.

Incorrect rows in results.
Steps to reproduce bug with incorrect offset:
1) Create new view with CSV data export.
2) set path, filename. Export Method: Batch, size 100, limit 101.
3) export with drush command
drush vde_drush:views-data-export view_name display_id /filepath/test.csv --yes

Result: in exported file you will have header more than 200 rows.

As I previosuly mentioned, I've changed data in queue item from views object to view_id and display_id.
This will allow use to execute query each time with correct offset and items per page.

Issue with queue items:
Queue can consists of more then one export when it's running in the same time.
For example you have a cron which use drush to export and at the same time you doing it manually from drush command.
That's why I've removed line
- $total_queue_items = $queue->numberOfItems() * $items_per_batch - $items_per_batch;
which makes no sense if there are more than one batch at the same time.