Fix the default value of the $length parameter of grapheme_substr()

Author: kocsismate

ext/intl/php_intl.stub.php

@@ -245,7 +245,7 @@ function grapheme_strrpos(string $haystack, string $needle, int $offset = 0): in
 
 function grapheme_strripos(string $haystack, string $needle, int $offset = 0): int|false {}
 
-function grapheme_substr(string $string, int $start, ?int $length = 0): string|false {}
+function grapheme_substr(string $string, int $start, ?int $length = null): string|false {}
 
 function grapheme_strstr(string $haystack, string $needle, bool $before_needle = false): string|false {}
 

ext/intl/php_intl_arginfo.h

@@ -463,7 +463,7 @@ ZEND_END_ARG_INFO()
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_MASK_EX(arginfo_grapheme_substr, 0, 2, MAY_BE_STRING|MAY_BE_FALSE)
 	ZEND_ARG_TYPE_INFO(0, string, IS_STRING, 0)
 	ZEND_ARG_TYPE_INFO(0, start, IS_LONG, 0)
-	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, length, IS_LONG, 1, "0")
+	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, length, IS_LONG, 1, "null")
 ZEND_END_ARG_INFO()
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_MASK_EX(arginfo_grapheme_strstr, 0, 2, MAY_BE_STRING|MAY_BE_FALSE)