Bug 10407: Resolve warnings from child process

Bug 10407: Resolve warnings from child process

After the staging job finishes, the child tries to print results to
STDOUT (which is closed). This creates warnings like:

stage-marc-import.pl: binmode() on closed filehandle STDOUT at C4/Templates.pm line 120.
stage-marc-import.pl: Filehandle STDOUT reopened as FH only for input at /usr/lib/perl5/Template/Provider.pm line 964.

Resolving it is simple: the child should exit after marking the job
as finished.

Test plan:
Import a marc file.
Observe that you do no longer have such warnings.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>