Fix GH-9697: array_walk($ffiInstance, function () {}) crashes due to expecting mutable array

Author: dstogov

ext/ffi/tests/gh9697.phpt

@@ -0,0 +1,14 @@
+--TEST--
+GH-9697 (array_walk($ffiInstance, function () {}) crashes due to expecting mutable array)
+--SKIPIF--
+<?php
+if (!extension_loaded("ffi")) die("skip ffi extension not available");
+?>
+--FILE--
+<?php
+$x = FFI::new('int');
+array_walk($x, function($x) { echo "test\n"; });
+?>
+DONE
+--EXPECT--
+DONE

ext/standard/array.c

@@ -1333,6 +1333,10 @@ static int php_array_walk(zval *array, zval *userdata, int recursive) /* {{{ */
 	uint32_t ht_iter;
 	int result = SUCCESS;
 
+	if (zend_hash_num_elements(target_hash) == 0) {
+		return result;
+	}
+
 	/* Set up known arguments */
 	ZVAL_UNDEF(&args[1]);
 	if (userdata) {