Add cautionary assert for divide-by-zero

[paulhauner]

What

Adds a cautionary assert for divide-by-zero on get_permutated_index

Why

[JustinDrake]

There is already is an implicit assert with the modulo

pivot = bytes_to_int(hash(seed + int_to_bytes1(round))[0:8]) % list_size

This produces

ZeroDivisionError: integer division or modulo by zero

[paulhauner]

My objective was to make it explicit.

Maybe I've been spending too much time in a language focused on safety.

[paulhauner]

Now I think about it, the spec is full of implicit asserts.

Happy to close this one.

[vbuterin]

Technically, we really should have an assert that index < list_size, which would implicitly require list_size > 0.

[paulhauner]

Technically, we really should have an assert that index < list_size, which would implicitly require list_size > 0.

I was just about to raise this actually! It still returns a result when index >= list_size.

Edit: just updated the PR accordingly.