ug 11857 - Number of patrons on a patron list not accurate

When creating a patron list with only 1 patron, the patron
lists page says that the list contains 3 patrons.
When creating a patron list with only 1 patron, it works fine.

This is caused by the fact that access on "patron_list_patrons"
Koha::Schema::Result::PatronList object returns an hash if one
result and an array if more results.
See similar problem at
http://permalink.gmane.org/gmane.comp.lang.perl.modules.template-toolkit/7250

This patch replaces by the call on resultset and then the use of
"count" method.

Test plan :
- Go to patron lists : /cgi-bin/koha/patron_lists/lists.pl
- Create a new patron list LIO
- Add one patron
- Create a new patron list LIM
- Add 2 patrons
- Go to patron lists : /cgi-bin/koha/patron_lists/lists.pl
=> Without this patch you see :
  Name  Patrons in list
  LIO   3
  LIM   2
=> With this patch you see :
  Name  Patrons in list
  LIO   1
  LIM   2

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Work as described, no koha-qa errors.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes all tests and QA script. Confirmed the problem and that
the patch fixes it.

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>