PHPStan found a error when the result of the `filter_var` function is compared with `false`

# Bug report

PHPStan 1.9.2

Why is an error thrown if a function `filter_var` returns `false` when filtering failed?

### Code snippet that reproduces the problem

https://phpstan.org/r/d01c48b0-59eb-4927-9a10-5459d2872646

### Expected output

[OK] No errors

