Error handling empty array

[TomCC7]

Although it's weird to store an empty array in the npz file (I forgot to delete that field :cry:), NPZ.jl will throw an error when it trys to unpack an npz file with empty array.

Steps to reproduce

• create an npz file with empty field

In [4]: a=np.load("aba.npz")

In [5]: a["a"]
Out[5]: array([], dtype=float64)

• in julia

julia> npzread("aba.npz")
ERROR: EOFError: read end of file
Stacktrace:
  [1] _read(f::ZipFile.ReadableFile, a::Vector{UInt8})
    @ ZipFile ~/.julia/packages/ZipFile/evaHP/src/ZipFile.jl:519
  [2] read!
    @ ~/.julia/packages/ZipFile/evaHP/src/ZipFile.jl:483 [inlined]
  [3] readheader(f::ZipFile.ReadableFile)
    @ NPZ ~/.julia/packages/NPZ/uRQRY/src/NPZ.jl:210
  [4] npzreadarray(f::ZipFile.ReadableFile)
    @ NPZ ~/.julia/packages/NPZ/uRQRY/src/NPZ.jl:243
  [5] (::NPZ.var"#4#7")(f::ZipFile.ReadableFile)
    @ NPZ ./none:0
  [6] iterate
    @ ./generator.jl:47 [inlined]
  [7] _all(f::Base.var"#318#320", itr::Base.Generator{Base.Iterators.Filter{NPZ.var"#5#8"{Vector{String}}, Vector{ZipFile.ReadableFile}}, NPZ.var"#4#7"}, #unused#::Colon)
    @ Base ./reduce.jl:1156
  [8] all
    @ ./reduce.jl:1152 [inlined]
  [9] Dict(kv::Base.Generator{Base.Iterators.Filter{NPZ.var"#5#8"{Vector{String}}, Vector{ZipFile.ReadableFile}}, NPZ.var"#4#7"})
    @ Base ./dict.jl:131
 [10] npzread (repeats 2 times)
    @ ~/.julia/packages/NPZ/uRQRY/src/NPZ.jl:311 [inlined]
 [11] npzread(::String)
    @ NPZ ~/.julia/packages/NPZ/uRQRY/src/NPZ.jl:295
 [12] top-level scope
    @ REPL[1]:1

caused by: EOFError: read end of file
Stacktrace:
  [1] _read(f::ZipFile.ReadableFile, a::Vector{Float64})
    @ ZipFile ~/.julia/packages/ZipFile/evaHP/src/ZipFile.jl:519
  [2] _npzreadarray(f::ZipFile.ReadableFile, hdr::NPZ.Header{Float64, 1, typeof(ltoh)})
    @ NPZ ~/.julia/packages/NPZ/uRQRY/src/NPZ.jl:0
  [3] npzreadarray(f::ZipFile.ReadableFile)
    @ NPZ ~/.julia/packages/NPZ/uRQRY/src/NPZ.jl:244
  [4] (::NPZ.var"#4#7")(f::ZipFile.ReadableFile)
    @ NPZ ./none:0
  [5] iterate
    @ ./generator.jl:47 [inlined]
  [6] grow_to!(dest::Dict{Any, Any}, itr::Base.Generator{Base.Iterators.Filter{NPZ.var"#5#8"{Vector{String}}, Vector{ZipFile.ReadableFile}}, NPZ.var"#4#7"})
    @ Base ./dict.jl:140
  [7] dict_with_eltype
    @ ./abstractdict.jl:550 [inlined]
  [8] Dict(kv::Base.Generator{Base.Iterators.Filter{NPZ.var"#5#8"{Vector{String}}, Vector{ZipFile.ReadableFile}}, NPZ.var"#4#7"})
    @ Base ./dict.jl:129
  [9] npzread (repeats 2 times)
    @ ~/.julia/packages/NPZ/uRQRY/src/NPZ.jl:311 [inlined]
 [10] npzread(::String)
    @ NPZ ~/.julia/packages/NPZ/uRQRY/src/NPZ.jl:295
 [11] top-level scope
    @ REPL[1]:1