`EntryOptions::stack_index` panics when stack index is not set (when `Debug` is called on `EntryOptions`)

[ChocolateLoverRaj]

fn stack_index(&self) -> u16 {
    self.bits.get_bits(0..3) - 1
}

Here the - 1 causes a "attempt to subtract with overflow" error.

It's very easy to reproduce a panic:

log::info!("IDT: {:#?}", idt);

Probably caused by the +1 -1 translation stuff but I don't really understand why the translation is there and how the IDT encoding works.

[phil-opp]

Thanks for reporting! I think this was fixed already in #522, but not released yet.