Fix check if class exists

lib/private/backgroundjob/joblist.php

@@ -152,7 +152,7 @@ class JobList implements IJobList {
 		if ($class === 'OC_Cache_FileGlobalGC') {
 			$class = '\OC\Cache\FileGlobalGC';
 		}
-		if (class_exists($class)) {
+		if (!class_exists($class)) {
 			// job from disabled app or old version of an app, no need to do anything
 			return null;
 		}