can't cat two empty vectors

[bjarthur]

thanks for fixing #595. cat works now if one input argument is empty. but, it's still broken if they all are:

julia> using DimensionalData

julia> c=rand(X(Int64[]))
╭───────────────────────────────╮
│ 0-element DimArray{Float64,1} │
├───────────────────────────────┴──────────── dims ┐
  ↓ X Sampled{Int64} [] Unordered Irregular Points
└──────────────────────────────────────────────────┘

julia> cat(c,c,dims=X)
ERROR: ArgumentError: tuple must be non-empty
Stacktrace:
  [1] first(::Tuple{})
    @ Base ./tuple.jl:196
  [2] _check_cat_lookup_order(::Type)
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:434
  [3] _check_cat_lookup_order(D::Type, lookups::DimensionalData.Dimensions.Lookups.Sampled{…})
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:435
  [4] _check_cat_lookup_order(::Type, ::DimensionalData.Dimensions.Lookups.Sampled{…}, ::Vararg{…})
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:435
  [5] _check_cat_lookups(D::Type, l1::DimensionalData.Dimensions.Lookups.Sampled{…}, lookups::DimensionalData.Dimensions.Lookups.Sampled{…})
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:398
  [6] check_cat_lookups(::X{DimensionalData.Dimensions.Lookups.Sampled{…}}, ::Vararg{DimensionalData.Dimensions.Dimension})
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:390
  [7] (::DimensionalData.var"#197#204"{DimVector{…}, Tuple{…}})(catdim::Type)
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:296
  [8] map
    @ ./tuple.jl:291 [inlined]
  [9] _cat(catdims::Tuple{…}, A1::DimVector{…}, As::DimVector{…})
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:273
 [10] _cat(catdim::Type{…}, A1::DimVector{…}, As::DimVector{…})
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:269
 [11] cat(A1::DimVector{…}, As::DimVector{…}; dims::Type)
    @ DimensionalData ~/.julia/packages/DimensionalData/bjXdf/src/array/methods.jl:266
 [12] top-level scope
    @ REPL[12]:1
Some type information was truncated. Use `show(err)` to see complete types.

julia> a=rand(X([1,2,3]))
╭───────────────────────────────╮
│ 3-element DimArray{Float64,1} │
├───────────────────────────────┴──────────────────────── dims ┐
  ↓ X Sampled{Int64} [1, 2, 3] ForwardOrdered Irregular Points
└──────────────────────────────────────────────────────────────┘
 1  0.896782
 2  0.828088
 3  0.292937

julia> cat(a,c,c,dims=X)
╭───────────────────────────────╮
│ 3-element DimArray{Float64,1} │
├───────────────────────────────┴──────────────────────── dims ┐
  ↓ X Sampled{Int64} [1, 2, 3] ForwardOrdered Irregular Points
└──────────────────────────────────────────────────────────────┘
 1  0.896782
 2  0.828088
 3  0.292937

julia> VERSION
v"1.10.2"

julia> versioninfo()
Julia Version 1.10.2
Commit bd47eca2c8a (2024-03-01 10:14 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: macOS (arm64-apple-darwin22.4.0)
  CPU: 12 × Apple M2 Max
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, apple-m1)
Threads: 1 default, 0 interactive, 1 GC (on 8 virtual cores)
Environment:
  JULIA_PROJECT = @.
  JULIA_EDITOR = vi

[rafaqz]

Ahh damn, cat has been so much whack-a-mole