[BUGFIX] Make getExtensionConfiguration return empty array on failure

Classes/Utility/ExtensionUtility.php

@@ -43,11 +43,12 @@ class ExtensionUtility {
 	 */
 	public static function getExtensionConfiguration(): array {
 		if (version_compare(VersionNumberUtility::getCurrentTypo3Version(), '9.0.0', '<')) {
-			return \unserialize(
+			$extConf = \unserialize(
 				$GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf']['sg_mail'], ['allowed_classes' => FALSE]
 			);
-		} else {
-			return $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['sg_mail'];
+			return $extConf ?? [];
 		}
+
+		return $GLOBALS['TYPO3_CONF_VARS']['EXTENSIONS']['sg_mail'] ?? [];
 	}
 }