Bug 13109: Serial failure for received and general viewing.

Bug 13109: Serial failure for received and general viewing.

to test...

1/ attempt to view a subscription-detail that has a NULL value for either it's 'startdate' or 'enddate'

  an example url would be...
  http://koha-admin.foo.org/cgi-bin/koha/serials/subscription-detail.pl?subscriptionid=1

  observe error...
  'Date::Calc::PP::Delta_Days(): Usage: Date::Calc::Delta_Days($year1,$month1,$day1,$year2,$month2,$day2) at /your/koha/C4/Serials.pm line 2325'

2/ apply patch
3/ repeat step 1/
   observe that detail page displays OK

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
I confirm the issue if startdate is null (can exist with old data,
before the js check on the form).
Amended patch: Remove trailing space char and the link to the bz number
(can be found using git log).

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>