[php-src] Issue #8661: Inconsistency between null safe operator and property fetch with null coalesce

Issue: https://github.com/php/php-src/issues/8661 Author: rajyan ### Description Noticed this issue while investigating https://github.com/phpstan/phpstan/issues/7291. The following code: ```php <?php echo $a?->foo; echo $a?->foo ?? ''; echo isset($a?->foo); echo $a->foo; echo $a->foo ?? ''; echo isset($a->foo); ``` Resulted in this output: ``` Warning: Undefined variable $a in /in/bgVKX on line 3 Warning: Undefined variable $a in /in/bgVKX on line 4 Warning: Undefined variable $a in /in/bgVKX on line 7 Warning: Attempt to read property "foo" on null in /in/bgVKX on line 7 ``` But I expected this output instead: ``` Warning: Undefined variable $a in /in/bgVKX on line 3 Warning: Undefined variable $a in /in/bgVKX on line 7 Warning: Attempt to read property "foo" on null in /in/bgVKX on line 7 ``` I think line 4 should not report a warning because the undefined var $a is handled by null coalescing operator like in line 8. I believe it is a bug, because the inconsistency between line 4 and 5 (null coalesce vs isset), line 4 and line 8 (null safe vs non null safe) is hard to expect. ### PHP Version PHP 8.0.1 - 8.1.6 ### Operating System _No response_