Fix GH-16359 curl write callback crash on FCC usage w/o user function.

Author: devnexen

Zend/zend_API.h

@@ -843,6 +843,12 @@ static zend_always_inline void zend_call_known_fcc(
 	const zend_fcall_info_cache *fcc, zval *retval_ptr, uint32_t param_count, zval *params, HashTable *named_params)
 {
 	zend_function *func = fcc->function_handler;
+	if (UNEXPECTED(!func)) {
+		if (retval_ptr) {
+			ZVAL_UNDEF(retval_ptr);
+		}
+		return;
+	}
 	/* Need to copy trampolines as they get released after they are called */
 	if (UNEXPECTED(func->common.fn_flags & ZEND_ACC_CALL_VIA_TRAMPOLINE)) {
 		func = (zend_function*) emalloc(sizeof(zend_function));

ext/curl/tests/gh16359.phpt

@@ -0,0 +1,17 @@
+--TEST--
+GH-16360 - curl_setopt with CURLOPT_WRITEFUNCTION and no user fn
+--EXTENSIONS--
+curl
+--FILE--
+<?php
+$log_file = tempnam(sys_get_temp_dir(), 'php-curl-CURLOPT_WRITEFUNCTION-trampoline');
+$fp = fopen($log_file, 'w+');
+fwrite($fp, "test");
+$ch = curl_init();
+curl_setopt($ch, CURLOPT_WRITEFUNCTION, null);
+curl_setopt($ch, CURLOPT_URL, 'file://' . $log_file);
+curl_exec($ch);
+echo "DONE";
+?>
+--EXPECT--
+DONE