Bug 25567: Prevent patron category type's categorycode to be created with ""

It must be NULL/undef, the default from the DB.

The method Koha::Patron::Attribute::Type->categorycode is not covered by tests!

To recreate:
Create a new patron attribute type, don't select a patron's category (and not repeatable or unique)
Go to the batch patron modification tool, enter a cardnumber, next.
=> boom!
Apply the patch, edit the patron attribute, save
Go to the batch patron modification tool, enter a cardnumber, next.
=> success!

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit 7ce6f78956)
Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>

admin/patron-attr-types.pl

@@ -144,6 +144,17 @@ sub add_update_attribute_type {
     my $template = shift;
     my $code = shift;
 
+    my $description               = $input->param('description');
+    my $repeatable                = $input->param('repeatable') ? 1 : 0;
+    my $unique_id                 = $input->param('unique_id') ? 1 : 0;
+    my $opac_display              = $input->param('opac_display') ? 1 : 0;
+    my $opac_editable             = $input->param('opac_editable') ? 1 : 0;
+    my $staff_searchable          = $input->param('staff_searchable') ? 1 : 0;
+    my $authorised_value_category = $input->param('authorised_value_category');
+    my $display_checkout          = $input->param('display_checkout') ? 1 : 0;
+    my $category_code             = $input->param('category_code') || undef;
+    my $class                     = $input->param('class');
+
     my $description = $input->param('description');
 
     my $attr_type;