[BUGFIX] Prevent method call on invalid task in scheduler

Resolves: #94355
Releases: master, 10.4
Change-Id: Ibff208cf5e2165664a8e03952d207ece76be31e3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70254
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/scheduler/Classes/Scheduler.php

@@ -346,13 +346,13 @@ public function fetchTask($uid = 0)
         }
         /** @var Task\AbstractTask $task */
         $task = unserialize($row['serialized_task_object']);
-        if ($task->getTaskGroup() === null) {
-            // Fix invalid task_group=NULL settings in order to avoid exceptions when saving on PostgreSQL
-            $task->setTaskGroup(0);
-        }
         if ($this->isValidTaskObject($task)) {
             // The task is valid, return it
             $task->setScheduler();
+            if ($task->getTaskGroup() === null) {
+                // Fix invalid task_group=NULL settings in order to avoid exceptions when saving on PostgreSQL
+                $task->setTaskGroup(0);
+            }
         } else {
             // Forcibly set the disable flag to 1 in the database,
             // so that the task does not come up again and again for execution