Bug 14646: (regression test) Koha::RecordProcessor only accepts one filter at a time

Bug 14646: (regression test) Koha::RecordProcessor only accepts one filter at a time

This patch introduces new tests to t/RecordProcessor.t so it tests for
creating processors with more than one filter. It does so by running

    my $processor = new Koha::RecordProcessor({
                            filters => ['Null','Dummy']
                        });

and testing the results.

To test:
- Apply the patch
- Run:
  $ prove t/RecordProcessor.t
=> FAIL: tests related to multiple filters fail.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>