fix: check if page has been unlocked already

Author: johannschopplich

classes/KirbyExtended/LockedPages.php

@@ -24,7 +24,7 @@ public static function isLocked(?Page $page): bool
         }
 
         $access = kirby()->session()->data()->get(LockedPages::SESSION_KEY, []);
-        if (isset($access[$protectedPage->id()])) {
+        if (in_array($protectedPage->id(), $access)) {
             return false;
         }