Bug 19797: [16.11.x] Restore alert subscribers

This patch fixes a bad conflict between bug 18726 and bug 10357.
The alerttype variable was not passed to the template on 16.11.x

Test plan:
- Add a subscription
- Make sure you set a notice template for 'notification' on the first page
- Go to the record in the OPAC
- Subscribe to email notifications from the Subscriptions tab > More detail
- Verify that the alert table in the database has the entry for the subscribed patron
- Verify that in the OPAC it now asks you to cancel subscription

Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>

opac/opac-alert-subscribe.pl

@@ -78,6 +78,7 @@ else {
         my $subscription = &GetSubscription($externalid);
         $template->param(
             "typeissue$op" => 1,
+            alerttype      => $alerttype,
             bibliotitle    => $subscription->{bibliotitle},
             notes          => $subscription->{notes},
             externalid     => $externalid,