[BUGFIX] Handle falsy return type when getting selected folder

The method `FileLinkHandler->getSelectedFolder()` may return either an
instance of `Folder` or a blunt `false`, where the latter case was not
properly handled. This issue is now fixed.

Resolves: #103116
Resolves: #103122
Releases: 11.5
Change-Id: I245517ee884b6320d6bc4e2abb5a8a16f485fc69
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82999
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>

typo3/sysext/core/Classes/Authentication/BackendUserAuthentication.php

@@ -1677,7 +1677,7 @@ static function ($value, $permission) use (&$finalUserPermissions) {
      * @param int $pid PageUid
      * @param string $table Table name
      * @param string $field Field name
-     * @return \TYPO3\CMS\Core\Resource\Folder|bool The default upload folder for this user
+     * @return \TYPO3\CMS\Core\Resource\Folder|false The default upload folder for this user
      */
     public function getDefaultUploadFolder($pid = null, $table = null, $field = null)
     {

typo3/sysext/recordlist/Classes/LinkHandler/FileLinkHandler.php

@@ -123,8 +123,8 @@ public function render(ServerRequestInterface $request)
 
         // Create upload/create folder forms, if a path is given
         $selectedFolder = $this->getSelectedFolder($this->expandFolder);
-        if ($selectedFolder->getStorage()->isFallbackStorage()) {
-            $selectedFolder = null;
+        if ($selectedFolder && $selectedFolder->getStorage()->isFallbackStorage()) {
+            $selectedFolder = false;
         }
 
         // Build the file upload and folder creation form
@@ -281,7 +281,7 @@ public function getScriptUrl()
      * Returns the currently selected folder, or th default upload folder
      *
      * @param string $folderIdentifier
-     * @return mixed the folder object or false if nothing was found
+     * @return Folder|false the folder object or false if nothing was found
      */
     protected function getSelectedFolder($folderIdentifier = '')
     {