Bug 20556: Marking ILL request as complete..

Bug 20556: Marking ILL request as complete..

When marking a request as complete, the status is updated internally
then the user to redirected to the view of the request.

Although the redirect header is sent, there is no exit to indicate that
the program flow should stop. As a result, an attempt is made to render
the template, which fails.

This patch simply adds the missing exit.

TEST PLAN
---------

- Create an ILL request
- "Manage request" > "Confirm request"
- "Mark completed"
- TEST: Ensure that no error is written to the error log upon clicking
"Mark completed"

Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>