Bug 20098: Inventory tool: CVS export: fix itemlost column

Bug 20098: Inventory tool: CVS export: fix itemlost column

It was mapped with "lost" instead of "itemlost".

== Test plan ==
1. Have a lost item
2. Go to staff:/cgi-bin/koha/tools/inventory.pl
3. Tick "Optional filters" → "items.itemlost" →
      "name of Authorized values for the lost state"
4. Tick "Export to CSV file"
5. Submit
6. Open the CSV
7. Check that the lost item is in the list
8. You should observe that the "Lost status" column is empty for all items
     This is the problem
9. Apply this patch
10. Click submit to re-export the CSV
11. Open the CSV
12. Check that the lost item is in the list
13. You should observe that the "Lost status" column now filled with the
      expected values.
14. Smile because it works! :D

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Maksim Sen <maksim@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>