debug_backtrace class access uses wrong index

[rafageist]

From PHPStan baseline: src/div.php line 9933.

Snippet:
= debug_backtrace(); = [0]['function']; if (isset(['class'])) { = ['class'] . '::' . ; }

$d is an array of frames; class should be checked on a frame index (e.g., $d[0]['class'] or $d[1]['class']).