fix semaphore guarding

Signed-off-by: Simon L <szaimen@e.mail.de>

diff --git a/lib/private/Preview/Generator.php b/lib/private/Preview/Generator.php
index 4a1270fa4a60be68575e5c2ffc22f4f640223a74..d936f1d65ad2a94e1305124be8f06b15da0474b2 100644 (file)
--- a/lib/private/Preview/Generator.php
+++ b/lib/private/Preview/Generator.php
@@ -244,7 +244,7 @@ class Generator {
         * @return bool
         */
        public static function unguardWithSemaphore($semId): bool {
-               if (!is_resource($semId) || !extension_loaded('sysvsem')) {
+               if ($semId === false || get_class($semId) !== 'SysvSemaphore' || !extension_loaded('sysvsem')) {
                        return false;
                }
                return sem_release($semId);