Bug 20866: Make ArticleRequests.t pass even if table is not empty

Bug 20866: Make ArticleRequests.t pass even if table is not empty

Previous patch from Marcel removed the data from article_requests, I do
not think it is a good idea to remove existing data, it could hide bugs.

This patch moves the count inside the subtest block in order to have the
correct value when these tests are executed.
Previous code was broken: Koha::Patron->store does not generate a
userid, and ->search_limited did not work correctly
(Koha::Patron->has_permission returned early because of the non-existing
userid, 'return unless $self->userid;');

Test plan:
[1] Create an article request.
[2] Run t/db_dependent/ArticleRequests.t

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>