[BUGFIX] Check if a valid logger is available in error handlers

If the logger for some reason couldn't be created by GeneralUtility
or causes an exception or error itself the triggered ErrorHandler or
ExceptionHandler must not try to use the (non-existing) logger.

Resolves: #84646
Releases: master, 8.7
Change-Id: I46ba22bf4141c37db6530912b9e34252d1fb462c
Reviewed-on: https://review.typo3.org/56598
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Sybille Peters <sypets@gmx.de>
Tested-by: Sybille Peters <sypets@gmx.de>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>

typo3/sysext/core/Classes/Error/AbstractExceptionHandler.php

@@ -75,10 +75,12 @@ protected function writeLogEntries(\Throwable $exception, $context)
         // caused by this. Therefor we cannot do any database operation,
         // otherwise this will lead into recurring exceptions.
         try {
-            $this->logger->critical($logTitle . ': ' . $logMessage, [
-                'TYPO3_MODE' => TYPO3_MODE,
-                'exception' => $exception
-            ]);
+            if ($this->logger) {
+                $this->logger->critical($logTitle . ': ' . $logMessage, [
+                    'TYPO3_MODE' => TYPO3_MODE,
+                    'exception' => $exception
+                ]);
+            }
             // Write error message to sys_log table
             $this->writeLog($logTitle . ': ' . $logMessage);
         } catch (\Exception $exception) {

typo3/sysext/core/Classes/Error/ErrorHandler.php

@@ -129,7 +129,9 @@ public function handleError($errorLevel, $errorMessage, $errorFile, $errorLine)
         $logTitle = 'Core: Error handler (' . TYPO3_MODE . ')';
         $message = $logTitle . ': ' . $message;
 
-        $this->logger->log(LogLevel::NOTICE - $severity, $message);
+        if ($this->logger) {
+            $this->logger->log(LogLevel::NOTICE - $severity, $message);
+        }
 
         // Write error message to TSlog (admin panel)
         $timeTracker = $this->getTimeTracker();