Fix arginfo

The second parameter of `imagexbm()` is nullable.

Author: cmb69

ext/gd/gd.stub.php

@@ -117,7 +117,7 @@ function imagecreatefrombmp(string $filename) {}
 function imagecreatefromtga(string $filename) {}
 #endif
 
-function imagexbm($im, string $filename, int $foreground = UNKNOWN): bool {}
+function imagexbm($im, ?string $filename, int $foreground = UNKNOWN): bool {}
 
 function imagegif($im, $to = NULL): bool {}
 

ext/gd/gd_arginfo.h

@@ -196,7 +196,7 @@ ZEND_END_ARG_INFO()
 
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_imagexbm, 0, 2, _IS_BOOL, 0)
 	ZEND_ARG_INFO(0, im)
-	ZEND_ARG_TYPE_INFO(0, filename, IS_STRING, 0)
+	ZEND_ARG_TYPE_INFO(0, filename, IS_STRING, 1)
 	ZEND_ARG_TYPE_INFO(0, foreground, IS_LONG, 0)
 ZEND_END_ARG_INFO()