Allow immediate processing of just prepared tasks in cron worker runner

Preparing simple worker tasks is super fast, because it just switches the state to null.
But the processing of just prepared tasks required the second worker run and also second cron run.
This change optimize the behavior and in case there is still time left it immediately starts processing the tasks.
[MAILPOET-4684]

mailpoet/lib/Cron/CronWorkerRunner.php

@@ -73,6 +73,8 @@ class CronWorkerRunner {
       foreach ($dueTasks as $task) {
         $this->prepareTask($worker, $task);
       }
+      // Re-fetch running tasks so that we can process tasks that were just prepared
+      $runningTasks = $this->getRunningTasks($worker);
       foreach ($runningTasks as $task) {
         $this->processTask($worker, $task);
       }