Fix BC break of zend_throw_exception

Author: twose

Zend/zend_exceptions.c

@@ -851,7 +851,7 @@ static zend_object *zend_throw_exception_zstr(zend_class_entry *exception_ce, ze
 
 ZEND_API ZEND_COLD zend_object *zend_throw_exception(zend_class_entry *exception_ce, const char *message, zend_long code) /* {{{ */
 {
-	zend_string *msg_str = zend_string_init(message, strlen(message), 0);
+	zend_string *msg_str = message ? zend_string_init(message, strlen(message), 0) : NULL;
 	zend_object *ex = zend_throw_exception_zstr(exception_ce, msg_str, code);
 	zend_string_release(msg_str);
 	return ex;