Bug 26098: Fix JS error on the fund list view when no fund displayed

Bug 26098: Fix JS error on the fund list view when no fund displayed

TypeError: this.data(...) is undefined
in jquery.treetable.js

Test plan:
Go to the fund list view
Select a filter that will return no result
=> With this patch applied there is no JS error in the console

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit b6cb3c2ba54c0e10c27f37a0d2dec4f2875f2ddd)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>