[BUGFIX] Fix notice for browse menu with no parent page

Fix a notice if a browse menu is being generated but no parent page
is available.

Resolves: #97608
Releases: main, 11.5
Change-Id: Id0674fddccf62e02febdfa7b609521d0db3114b1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74603


Tested-by: core-ci <typo3@b13.com>
Tested-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: crell <larry@garfieldtech.com>
Reviewed-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Reviewed-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>

typo3/sysext/frontend/Classes/ContentObject/Menu/AbstractMenuContentObject.php

@@ -992,7 +992,7 @@ abstract class AbstractMenuContentObject
                 $recArr['up'] = $this->sys_page->getPage($value_rec['pid']);
             }
             // If the 'up' item was NOT level 0 in rootline...
-            if ($recArr['up']['pid'] && $value_rec['pid'] != $this->tmpl->rootLine[0]['uid']) {
+            if (($recArr['up']['pid'] ?? 0) && $value_rec['pid'] != $this->tmpl->rootLine[0]['uid']) {
                 // The page record of "index".
                 $recArr['index'] = $this->sys_page->getPage($recArr['up']['pid']);
             }