Check if classes/method exists before trying to call them in background jobs

lib/private/backgroundjob/joblist.php

@@ -152,6 +152,10 @@ class JobList implements IJobList {
 		if ($class === 'OC_Cache_FileGlobalGC') {
 			$class = '\OC\Cache\FileGlobalGC';
 		}
+		if (class_exists($class)) {
+			// job from disabled app or old version of an app, no need to do anything
+			return null;
+		}
 		$job = new $class();
 		$job->setId($row['id']);
 		$job->setLastRun($row['last_run']);

lib/private/backgroundjob/legacy/queuedjob.php

@@ -13,6 +13,8 @@ class QueuedJob extends \OC\BackgroundJob\QueuedJob {
 		$class = $argument['klass'];
 		$method = $argument['method'];
 		$parameters = $argument['parameters'];
-		call_user_func(array($class, $method), $parameters);
+		if (is_callable(array($class, $method))) {
+			call_user_func(array($class, $method), $parameters);
+		}
 	}
 }

lib/private/backgroundjob/legacy/regularjob.php

@@ -10,6 +10,8 @@ namespace OC\BackgroundJob\Legacy;
 
 class RegularJob extends \OC\BackgroundJob\Job {
 	public function run($argument) {
-		call_user_func($argument);
+		if (is_callable($argument)) {
+			call_user_func($argument);
+		}
 	}
 }