[Beforerr]

Problem

Disk arrays with an empty axis cannot be read when DiskArrays picks their chunks itself:

using DiskArrays, DiskArrays.TestTypes
a = UnchunkedDiskArray(rand(3, 5))
Array(view(a, :, 1:0))                         # ArgumentError: Chunk sizes must be strictly positive
convert(Vector, UnchunkedDiskArray(zeros(0)))  # same

This shows up in practice with selections that match no records.

Root cause

Two places use an axis length as the chunk size, so an empty axis gets chunk size 0 and RegularChunks rejects it:

• estimate_chunksize, which eachchunk of such a view falls back to (also eachchunk(zeros(3, 0)), eachchunkof zero dimensional array should work #292);
• common_chunks, which gives broadcasts over only unchunked arrays one chunk spanning the array.

This is the zero chunk size discussed in #220, but produced by DiskArrays itself rather than by a backend's eachchunk fallback.

Fix

Clamp both to at least 1, as RegularChunks(max(s, 1), 0, s) is recommended for backends.

Fixes #292