abstain from using xmlCleanupParser

Depending on circumstances, usage of xmlCleanupParser can affect
the thread local storage, or even cause crashes in single threaded
programs. On shutdown the memory will be freed anyway, however
not using xmlCleanupParser helps to avoid possible shutdown
crashes.

Author: weltling

ext/libxml/libxml.c

@@ -752,7 +752,7 @@ PHP_LIBXML_API void php_libxml_shutdown(void)
 #if defined(LIBXML_SCHEMAS_ENABLED)
 		xmlRelaxNGCleanupTypes();
 #endif
-		xmlCleanupParser();
+		/* xmlCleanupParser(); */
 		zend_hash_destroy(&php_libxml_exports);
 
 		xmlSetExternalEntityLoader(_php_libxml_default_entity_loader);