cron: exit 1 on exception

Allows the caller to more easily respond to cron failures.

Signed-off-by: Stephen Michel <git@smichel.me>

cron.php

  * @author Steffen Lindner <mail@steffen-lindner.de>
  * @author Thomas Müller <thomas.mueller@tmit.eu>
  * @author Vincent Petry <vincent@nextcloud.com>
+ * @author Stephen Michel <git@smichel.me>
  *
  * @license AGPL-3.0
  *
 	exit();
 } catch (Exception $ex) {
 	\OC::$server->getLogger()->logException($ex, ['app' => 'cron']);
+	exit(1);
 } catch (Error $ex) {
 	\OC::$server->getLogger()->logException($ex, ['app' => 'cron']);
+	exit(1);
 }