[BUGFIX] Installtool blocked when session file is empty

When the session information is fetched from the file system it can
happen that the session file is empty.

We should check for the file length and only read it, when the file
length is larger then 0.

Change-Id: I8857efc54f76c56984bc3486064b622b05e488b8
Resolves: #79955
Releases: master
Reviewed-on: https://review.typo3.org/51835


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>

typo3/sysext/install/Classes/Service/SessionService.php

@@ -389,7 +389,10 @@ class SessionService implements \TYPO3\CMS\Core\SingletonInterface
             if ($fd = fopen($sessionFile, 'rb')) {
                 $lockres = flock($fd, LOCK_SH);
                 if ($lockres) {
-                    $content = fread($fd, filesize($sessionFile));
+                    $length = filesize($sessionFile);
+                    if ($length > 0) {
+                        $content = fread($fd, $length);
+                    }
                     flock($fd, LOCK_UN);
                 }
                 fclose($fd);