Fix iteration for 0-dimensional disk arrays

[sethaxen]

Fixes #289

[felixcremer]

Why is the index restricted to an Int?
According to the docstring of iterate this is supposed to be an Integer and that also works for normal Arrays.

[sethaxen]

Ah, I see now it doesn't even require the state be an Int (that's just for AbstractString). iterate(::Array, i)'s implementation has no type constraint on i and just uses it for bounds checking and indexing. Meanwhile, valid index types for AbstractArrays are CartesianIndex (implicitly not supported here due to the bounds check) or "non-boolean integer" (https://docs.julialang.org/en/v1/manual/arrays/#man-supported-index-types), so I think this would be more consistent with the Base method, as it will error whenever the Base method would error (namely, when a CartesianIndex or Bool is provided):

Suggested change

	_iterate_disk(a::AbstractArray{<:Any,0}, i::Int=1) = i == 1 ? (a[], 2) : nothing
	_iterate_disk(a::AbstractArray{<:Any,0}, i=1) = i == 1 ? (@inbounds a[i], 2) : nothing

[felixcremer]

There is one equal sign to much in your function definition. Apart from that this looks good.

[sethaxen]

Ah, seems removing the Int specialization causes ambiguity with the other method. I could also remove that specialization or add it back to this method.