Bug 19258: Prevent warns when writing off an individual fine

Bug 19258: Prevent warns when writing off an individual fine

The following warns are triggered when I click the Write Off button next
to an individual fine or charge:
CGI::param called in list context from package
CGI::Compile::ROOT::home_vagrant_kohaclone_members_pay_2epl line 171,
this can lead to vulnerabilities. See the warning in "Fetching the
value or values of a single named parameter" at
/usr/share/perl5/CGI.pm line 436. (this shows many times)
Use of uninitialized value in subroutine entry at
/usr/share/perl5/URI/Escape.pm line 184.

To test:
1) Go to a members detail page in staff side and create a manual
invoice
2) Go to the pay fines tab, click the Write off button next to the
invoice you just created
3) Notice warns
4) Apply patch and repeat steps 1 & 2
5) Warns should be gone

Sponsored-by: Catalyst IT
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>