phpstan: define LEVELDB_ZLIB_RAW_COMPRESSION if it doesn't exist (for phpstan)

this improves the analysis quality by informing phpstan of the type of whatever should be there.

tests/phpstan/bootstrap.php

@@ -23,6 +23,11 @@ declare(strict_types=1);
 
 define('pocketmine\_PHPSTAN_ANALYSIS', true);
 
+if(!defined('LEVELDB_ZLIB_RAW_COMPRESSION')){
+	//leveldb might not be loaded
+	define('LEVELDB_ZLIB_RAW_COMPRESSION', 4);
+}
+
 //TODO: these need to be defined properly or removed
 define('pocketmine\COMPOSER_AUTOLOADER_PATH', dirname(__DIR__, 2) . '/vendor/autoload.php');
 define('pocketmine\DATA', '');