[php-src] Issue #13681: phpdbg_watch null pointer access

Issue: https://github.com/php/php-src/issues/13681 Author: YuanchengJiang ### Description Given the following phpt: ``` --TEST-- phpdbg_watch null pointer access --SKIPIF-- <?php if (getenv('SKIP_ASAN')) { die("skip intentionally causes segfaults"); } ?> --FILE-- <?php $s = "123"; $s1 = "test"; $s2 = "45345some"; $s >>= 2; var_dump($s); try { $s1 >>= 1; var_dump($s1); } catch (\TypeError $e) { echo $e->getMessage() . \PHP_EOL; } $s2 >>= 3; var_dump($s2); echo "Done\n"; ?> <?php $a = []; $a[0] = 1; $a[0] = 2; $a = [0 => 3, 1 => 4]; --PHPDBG-- b 6 r w a $a c q --EXPECTF-- int(30) Unsupported operand types: string >> int Warning: A non-numeric value encountered in %s on line %d int(5668) Done [Successful compilation of %s] prompt> [Breakpoint #0 added at %s:6] prompt> [Breakpoint #0 at %s:6, hits: 1] >00006: $a[0] = 2; 00007: 00008: $a = [0 => 3, 1 => 4]; prompt> [Added watchpoint #0 for $a[]] prompt> [Breaking on watchpoint $a[]] 1 elements were added to the array >00009: prompt> [$a[] has been removed, removing watchpoint] [Script ended normally] prompt> ``` Resulted in this output: ``` /WorkSpace/php-src/sapi/phpdbg/phpdbg_watch.c:969:41: runtime error: member access within null pointer of type 'phpdbg_watchpoint_t' (aka 'struct _phpdbg_watchpoint_t') SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /WorkSpace/php-src/sapi/phpdbg/phpdbg_watch.c:969:41 in ``` ### PHP Version PHP 8.4.0-dev ### Operating System ubuntu 22.04