out of bounds error on empty iterator indexing

[lmiq]

This PR aims to fix #58 by considering out-of-bounds indexing of the chunk iterator an error even if the iterator is empty.

Obs: Checked that all OhMyThreads tests passed.

Previously:

julia> chunks(Float64[]; n=2)[1]
0-element view(::Vector{Float64}, 0:-1) with eltype Float64

julia> chunks(0:-1; n=2)[1]
-1:-2

Now:

julia> chunks(Float64[]; n=2)[1]
ERROR: ArgumentError: chunk index out of bounds: 1 not in 1:0 (length=0)

julia> chunks(0:-1; n=2)[1]
ERROR: ArgumentError: chunk index out of bounds: 1 not in 1:0 (length=0)

[lmiq]

These changes are important to allow eltype to return the proper types without having to call getchunkindices. firstindex and lastindex are considered part of the required interface.

[lmiq]

@carstenbauer

Want to take a look? I think this is more consistent throwing an error for empty iterators and can be considered a bug-fix.

OhMyThreads.jl tests are not affected.

[carstenbauer]

Haven't look at this in detail, but why are you throwing an ArgumentError rather than an BoundsError?

[lmiq]

Haven't look at this in detail, but why are you throwing an ArgumentError rather than an BoundsError?

The "historical" reason is that this error was reached when the chunks object was constructed, not only when indexing into it.

Now, we can turn that into a BoundsError, at the cost of having a less specific error message, but probably that's for the best. Updated it now.

[nhz2]

Yes, this fixes #58
I also think the docstrings of chunks and index_chunks could be updated to indicate that the default minsize is 1.