Avoid infinite loop in readbytes!(s, UInt8[], 1)

[nhz2]

Fixes #193
This fixes the edge case of calling readbytes! with an empty b but non-zero nb by resizing b initially to 32 bytes if b is too small.

[mkitti]

Why 32? Should we make it a constant somewhere?

[nhz2]

Just a small number, readbytes! is usually called with a 1024 byte buffer in read so this issue usually isn't a problem: https://github.com/JuliaLang/julia/blob/v1.9.4/base/io.jl#L1000

I looked in resize! and if understand this correctly, https://github.com/JuliaLang/julia/blob/4ee10228176c960fc3d0046390ab2ef4df7ab08a/base/array.jl#L1040-L1041 seems to resize to a minimum of 8 bytes so I think I'll change 32 to 8 here as well.