Bug 17842: Simplify the code

Bug 17842: Simplify the code

There is no need for all the conditions.
From Encode::encode POD:
  "If the $string is undef, then undef is returned."

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 74c7530e3dacd7a1df9ed72d031bc1a5b7063142)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit 6802d1a67e47fae0982c969f414b05f4f6a7cc28)

Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
(cherry picked from commit 4809536e8f561ea708264b80d415b10b4703a9fd)
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>