Offset 1|2 does not exist on array{1?: type, 2?: type} after safety-check by array_key_exists is performed

# Bug report

Tested on 1.8.2

### Code snippet that reproduces the problem

https://phpstan.org/r/f4e1ed64-c315-4618-94c7-8cda6151dca4

### Expected output

No error