Bug 26983: Fix [un]select all links in inventory

Bug 26983: Fix [un]select all links in inventory

The select/unselect all links took into account only the items displayed
when the page was loaded (so 20).

Test plan:
1. Go to Tools-> Inventory-> Do a Search to produce more than 20 results
2. Select 50, 100 or All entries to show
3. click on Select All
=> All items must be selected, not only the first 20

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>