[BUGFIX] Ensure output compression handler is only initialized once

The middleware `SudoModeInterceptor::handleRequestGrantedException()`
invokes `TYPO3\CMS\Core\Http\Application` again when picking up the
previous HTTP non-GET request. This triggers the initialization of the
`OutputCompression` middleware again, causing a PHP warning concerning
the active `ob_gzhandler`.

Resolves: #106785
Releases: main, 13.4, 12.4
Change-Id: I4928a81f3e60a35f18dcaee6112feaf36600a36c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/91321
Reviewed-by: Sebastian Iffland <sebastian.iffland@fullhaus.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: Oliver Hader <oliver.hader@typo3.org>

Author: ohader

typo3/sysext/backend/Classes/Middleware/OutputCompression.php

@@ -52,7 +52,9 @@ protected function initializeOutputCompression(): void
             if (MathUtility::canBeInterpretedAsInteger($GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel'])) {
                 @ini_set('zlib.output_compression_level', (string)$GLOBALS['TYPO3_CONF_VARS']['BE']['compressionLevel']);
             }
-            ob_start('ob_gzhandler');
+            if (!in_array('ob_gzhandler', ob_list_handlers(), true)) {
+                ob_start('ob_gzhandler');
+            }
         }
     }
 }