Bug 22442: (bug 13618 follow-up) Fix item search CSV export

Bug 22442: (bug 13618 follow-up) Fix item search CSV export

We must not filter assignements statements.

Test plan:
Export item search result as CSV
Without this patch the biblio and biblioitem values are not displayed.
With this patch applied everything is displayed correctly

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit bb730c1b05c91ee92db09d117293a0ddb87dace1)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>