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>

tools/stage-marc-import.pl

@@ -175,6 +175,7 @@ if ($completedJobID) {
     };
     if ($runinbackground) {
         $job->finish($results);
+        exit 0;
     } else {
 	    $template->param(staged => $num_valid,
  	                     matched => $num_with_matches,