Bug 15832: Remove empty string from the filters

Bug 15832: Remove empty string from the filters

On each cell, the split will generate a new empty entry.
This patch removes that entry.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan Gallagher <bredan@bywatersolutions.com>
(cherry picked from commit 1931ff465317aa2bf8d31c0c817ff0c4d75ea8dc)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
(cherry picked from commit ef6c60d8ccc93832f87f7b6fe1f3daa5ce48dda9)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>