[php-src] Issue #13856: Member access within null pointer of type 'ps_files' in ext/session/mod_files.c

Issue: https://github.com/php/php-src/issues/13856 Author: YuanchengJiang ### Description The following code: ```php <?php class CustomReadHandler extends \SessionHandler { public function read($session_id): string|false { return parent::read('mycustomsession'); } } ob_start(); session_set_save_handler(new CustomReadHandler(), true); session_start(); ?> ``` Resulted in this output: ``` /php-src/ext/session/mod_files.c:140:12: runtime error: member access within null pointer of type 'ps_files' SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /php-src/ext/session/mod_files.c:140:12 in ``` To reproduce: ``` /php-src/sapi/cli/php -n -c '/php-src/tmp-php.ini' -d "opcache.cache_id=worker20" -d "output_handler=" -d "open_basedir=." -d "disable_functions=" -d "output_buffering=Off" -d "error_reporting=32767" -d "display_errors=1" -d "display_startup_errors=1" -d "log_errors=0" -d "html_errors=0" -d "track_errors=0" -d "report_memleaks=1" -d "report_zend_debug=0" -d "docref_root=" -d "docref_ext=.html" -d "error_prepend_string=" -d "error_append_string=" -d "auto_prepend_file=" -d "auto_append_file=" -d "ignore_repeated_errors=0" -d "precision=14" -d "serialize_precision=-1" -d "memory_limit=128M" -d "opcache.fast_shutdown=0" -d "opcache.file_update_protection=0" -d "opcache.revalidate_freq=0" -d "opcache.jit_hot_loop=1" -d "opcache.jit_hot_func=1" -d "opcache.jit_hot_return=1" -d "opcache.jit_hot_side_exit=1" -d "opcache.jit_max_root_traces=100000" -d "opcache.jit_max_side_traces=100000" -d "opcache.jit_max_exit_counters=100000" -d "opcache.protect_memory=1" -d "zend.assertions=1" -d "zend.exception_ignore_args=0" -d "zend.exception_string_param_max_len=15" -d "short_open_tag=0" -d "extension_dir=/php-src/modules/" -d "zend_extension=/php-src/modules/opcache.so" -d "session.auto_start=0" -d "session.save_handler=files" -d "session.save_path=" -d "session.use_strict_mode=0" -f "/php-src/tests/test.php" 2>&1 ``` ### PHP Version PHP 8.4.0-dev ### Operating System ubuntu 22.04