[BUG] `contract` fails for zerodim input

[ogauthe]

Thanks for #15 . I find there is still a problem for zero-dim input:

contract((1,), ones((1,)), (1,), ones(()), ())

ERROR: MethodError: no method matching output_axes(::typeof(contract), ::TensorAlgebra.BlockedPermutation{…}, ::Vector{…}, ::TensorAlgebra.BlockedPermutation{…}, ::Array{…}, ::TensorAlgebra.BlockedPermutation{…}, ::Bool)
The function `output_axes` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  output_axes(::typeof(contract), ::TensorAlgebra.BlockedPermutation{1}, ::AbstractArray, ::TensorAlgebra.BlockedPermutation{1}, ::AbstractArray, ::TensorAlgebra.BlockedPermutation{2}, ::Number)
   @ TensorAlgebra ~/Documents/itensor/TensorAlgebra.jl/src/contract/allocate_output.jl:39
  output_axes(::typeof(contract), ::TensorAlgebra.BlockedPermutation{2}, ::AbstractArray, ::TensorAlgebra.BlockedPermutation{1}, ::AbstractArray, ::TensorAlgebra.BlockedPermutation{1}, ::Number)
   @ TensorAlgebra ~/Documents/itensor/TensorAlgebra.jl/src/contract/allocate_output.jl:71
  output_axes(::typeof(contract), ::TensorAlgebra.BlockedPermutation{1}, ::AbstractArray, ::TensorAlgebra.BlockedPermutation{2}, ::AbstractArray, ::TensorAlgebra.BlockedPermutation{1}, ::Number)
   @ TensorAlgebra ~/Documents/itensor/TensorAlgebra.jl/src/contract/allocate_output.jl:55
  ...

Stacktrace:
 [1] allocate_output(::typeof(contract), biperm_dest::TensorAlgebra.BlockedPermutation{…}, a1::Vector{…}, biperm1::TensorAlgebra.BlockedPermutation{…}, a2::Array{…}, biperm2::TensorAlgebra.BlockedPermutation{…}, α::Bool)
   @ TensorAlgebra ~/Documents/itensor/TensorAlgebra.jl/src/contract/allocate_output.jl:97
 [2] contract(alg::TensorAlgebra.Matricize, biperm_dest::TensorAlgebra.BlockedPermutation{…}, a1::Vector{…}, biperm1::TensorAlgebra.BlockedPermutation{…}, a2::Array{…}, biperm2::TensorAlgebra.BlockedPermutation{…}, α::Bool; kwargs::@Kwargs{})
   @ TensorAlgebra ~/Documents/itensor/TensorAlgebra.jl/src/contract/contract.jl:121
 [3] contract(alg::TensorAlgebra.Matricize, biperm_dest::TensorAlgebra.BlockedPermutation{…}, a1::Vector{…}, biperm1::TensorAlgebra.BlockedPermutation{…}, a2::Array{…}, biperm2::TensorAlgebra.BlockedPermutation{…}, α::Bool)
   @ TensorAlgebra ~/Documents/itensor/TensorAlgebra.jl/src/contract/contract.jl:111
 [4] contract(alg::TensorAlgebra.Matricize, labels_dest::Tuple{Int64}, a1::Vector{Float64}, labels1::Tuple{Int64}, a2::Array{Float64, 0}, labels2::Tuple{}, α::Bool; kwargs::@Kwargs{})
   @ TensorAlgebra ~/Documents/itensor/TensorAlgebra.jl/src/contract/contract.jl:92
 [5] contract
   @ ~/Documents/itensor/TensorAlgebra.jl/src/contract/contract.jl:81 [inlined]
 [6] #contract#29
   @ ~/Documents/itensor/TensorAlgebra.jl/src/contract/contract.jl:62 [inlined]
 [7] contract
   @ ~/Documents/itensor/TensorAlgebra.jl/src/contract/contract.jl:52 [inlined]
 [8] contract(labels_dest::Tuple{Int64}, a1::Vector{Float64}, labels1::Tuple{Int64}, a2::Array{Float64, 0}, labels2::Tuple{})
   @ TensorAlgebra ~/Documents/itensor/TensorAlgebra.jl/src/contract/contract.jl:52
 [9] top-level scope
   @ REPL[16]:1
Some type information was truncated. Use `show(err)` to see complete types.

[mtfishman]

Thanks for the report, that should be easy to fix.