Bug: False positive for a problem already checked with an `if` (here with `strpos()`)

[ThomasLandauer]

See https://psalm.dev/r/863d8d0859
In the top function this error is emitted:

Left operand cannot be falsable, got false|int<0, max>

The bottom function does the same, but has no error.

In this case, strpos() is used, but I guess it's a more general issue...

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/863d8d0859

<?php

function foo(string $haystack, string $needle): int
{
    if (is_int(strpos($haystack, $needle))) {
        return strpos($haystack, $needle) - 1;
    }
    return 0;
}

function bar(string $haystack, string $needle): int
{
    $pos = strpos($haystack, $needle);
    if (is_int($pos)) {
        return $pos - 1;
    }
    return 0;
}

Psalm output (using commit cdceda0):

ERROR: PossiblyFalseOperand - 6:16 - Left operand cannot be falsable, got false|int<0, max>