Bug 15209: Check the parameter at the beginning of the subroutines

 Bug 15209: Check the parameter at the beginning of the subroutines

It seems better to check if parameters exist at the beginning of a
subroutine.
It makes the code easier to read and there is 1 indentation level less.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit 372881ebfd5552ecb83450c7afea6a76f2df1a0b)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>