[BUGFIX] Avoid undefined array key access

The LogManager tries to access $GLOBALS['TYPO3_CONF_VARS']['LOG']
without considering that it could be undefined

Releases: main, 11.5
Resolves: #97888
Change-Id: I7ac2435e548e2d241fe223686595a42927ae1a60
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75068


Tested-by: core-ci <typo3@b13.com>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>

typo3/sysext/core/Classes/Log/LogManager.php

@@ -196,7 +196,7 @@ class LogManager implements SingletonInterface, LogManagerInterface
         // Search in the $TYPO3_CONF_VARS['LOG'] array
         // for these keys, for example "writerConfiguration"
         $configurationKey = $configurationType . 'Configuration';
-        $configuration = $GLOBALS['TYPO3_CONF_VARS']['LOG'];
+        $configuration = $GLOBALS['TYPO3_CONF_VARS']['LOG'] ?? [];
         $result = $configuration[$configurationKey] ?? [];
         // Walk from general to special (t3lib, t3lib.db, t3lib.db.foo)
         // and search for the most specific configuration