fix: library entries read as not found without the library right (P12)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/Integrations/Divi/Library/LibraryAccess.php

@@ -51,7 +51,9 @@ class LibraryAccess
     /**
      * The library entry $postId after the checks for reading, or their refusal; null when $postId
      * names no library entry (the caller goes on with PostGuard). With the library hidden (ruling
-     * P9), an entry is refused exactly like an ID that does not exist – before any rights check.
+     * P9) or without the library right at all (ruling P12), an entry is refused exactly like an ID
+     * that does not exist, so its type and existence stay unknown; only a user with the library
+     * right who lacks edit_post on the entry gets forbidden (like pages).
      */
     public function item(mixed $postId, bool $forWrite): WP_Post|WP_Error|null
     {
@@ -61,7 +63,7 @@ class LibraryAccess
             return null;
         }
 
-        if ($this->visible !== null && ! ($this->visible)()) {
+        if (($this->visible !== null && ! ($this->visible)()) || $this->canList() !== null) {
             return PostGuard::notFound((int) $post->ID);
         }