fix null pointer dereference in php_mail_detect_multiple_crlf via error_log

Author: jordikroon

ext/standard/basic_functions.c

@@ -1353,7 +1353,9 @@ PHPAPI zend_result _php_error_log(int opt_err, const zend_string *message, const
 	switch (opt_err)
 	{
 		case 1:		/*send an email */
-			if (!php_mail(ZSTR_VAL(opt), "PHP error_log message", ZSTR_VAL(message), ZSTR_VAL(headers), NULL)) {
+			const char *to = opt ? ZSTR_VAL(opt) : NULL;
+			const char *hdrs = headers ? ZSTR_VAL(headers) : NULL;
+			if (!php_mail(to, "PHP error_log message", ZSTR_VAL(message), hdrs, NULL)) {
 				return FAILURE;
 			}
 			break;

tests/basic/gh20858.phpt

@@ -0,0 +1,8 @@
+--TEST--
+GH-20858 Null pointer dereference in php_mail_detect_multiple_crlf via error_log
+--FILE--
+<?php
+error_log(0, 1, null);
+?>
+--EXPECTF--
+sendmail: fatal: %r[^()]+%r(%d): No recipient addresses found in message header