offsetAccess.nonOffsetAccessible suppressed by isset

### Bug report

`Error` exception is raised but no warning from SA.

### Code snippet that reproduces the problem

https://phpstan.org/r/4ade25a7-da2a-40ae-b3e3-89713d804052

### Expected output

Cannot access offset 'a' on stdClass.

### Did PHPStan help you today? Did it make you happy in any way?

_No response_