Can't differentiate the constant basis function in Chebyshev()^2

[tobydriscoll]

I expected this to just return zero:

julia> X = Chebyshev()^2;

julia> f = Fun(X,[1.0]);

julia> D = Derivative(X,[1,0]);

julia> D*f
ERROR: BoundsError: attempt to access 0-element UnitRange{Int64} at index [0]
Stacktrace:
 [1] throw_boundserror(A::UnitRange{Int64}, I::Int64)
   @ Base ./abstractarray.jl:651
 [2] getindex
   @ ./range.jl:696 [inlined]
 [3] mul_coefficients(A::ApproxFunBase.SubOperator{Float64, KroneckerOperator{ApproxFunBase.ConcreteDerivative{Chebyshev{ChebyshevInterval{Float64}, Float64}, Int64, Float64}, ConstantOperator{Float64, Chebyshev{ChebyshevInterval{Float64}, Float64}}, TensorSpace{Tuple{Chebyshev{ChebyshevInterval{Float64}, Float64}, Chebyshev{ChebyshevInterval{Float64}, Float64}}, DomainSets.VcatDomain{2, Float64, (1, 1), Tuple{ChebyshevInterval{Float64}, ChebyshevInterval{Float64}}}, Float64}, TensorSpace{Tuple{Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}, Chebyshev{ChebyshevInterval{Float64}, Float64}}, DomainSets.VcatDomain{2, Float64, (1, 1), Tuple{ChebyshevInterval{Float64}, ChebyshevInterval{Float64}}}, Float64}, ApproxFunBase.CachedIterator{Tuple{Int64, Int64}, ApproxFunBase.Tensorizer{Tuple{FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}, FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}}}}, ApproxFunBase.CachedIterator{Tuple{Int64, Int64}, ApproxFunBase.Tensorizer{Tuple{FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}, FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}}}}, Float64}, Tuple{UnitRange{Int64}, UnitRange{Int64}}, Tuple{Int64, Int64}, Tuple{Int64, Int64}}, b::Vector{Float64})
   @ ApproxFunBase ~/.julia/packages/ApproxFunBase/BW4ev/src/PDE/KroneckerOperator.jl:421
 [4] mul_coefficients
   @ ~/.julia/packages/ApproxFunBase/BW4ev/src/Operators/general/algebra.jl:590 [inlined]
 [5] mul_coefficients(A::ApproxFunBase.DerivativeWrapper{KroneckerOperator{ApproxFunBase.ConcreteDerivative{Chebyshev{ChebyshevInterval{Float64}, Float64}, Int64, Float64}, ConstantOperator{Float64, Chebyshev{ChebyshevInterval{Float64}, Float64}}, TensorSpace{Tuple{Chebyshev{ChebyshevInterval{Float64}, Float64}, Chebyshev{ChebyshevInterval{Float64}, Float64}}, DomainSets.VcatDomain{2, Float64, (1, 1), Tuple{ChebyshevInterval{Float64}, ChebyshevInterval{Float64}}}, Float64}, TensorSpace{Tuple{Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}, Chebyshev{ChebyshevInterval{Float64}, Float64}}, DomainSets.VcatDomain{2, Float64, (1, 1), Tuple{ChebyshevInterval{Float64}, ChebyshevInterval{Float64}}}, Float64}, ApproxFunBase.CachedIterator{Tuple{Int64, Int64}, ApproxFunBase.Tensorizer{Tuple{FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}, FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}}}}, ApproxFunBase.CachedIterator{Tuple{Int64, Int64}, ApproxFunBase.Tensorizer{Tuple{FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}, FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}}}}, Float64}, TensorSpace{Tuple{Chebyshev{ChebyshevInterval{Float64}, Float64}, Chebyshev{ChebyshevInterval{Float64}, Float64}}, DomainSets.VcatDomain{2, Float64, (1, 1), Tuple{ChebyshevInterval{Float64}, ChebyshevInterval{Float64}}}, Float64}, Vector{Int64}, Float64}, b::Vector{Float64})
   @ ApproxFunBase ~/.julia/packages/ApproxFunBase/BW4ev/src/Operators/Operator.jl:490
 [6] *(A::ApproxFunBase.DerivativeWrapper{KroneckerOperator{ApproxFunBase.ConcreteDerivative{Chebyshev{ChebyshevInterval{Float64}, Float64}, Int64, Float64}, ConstantOperator{Float64, Chebyshev{ChebyshevInterval{Float64}, Float64}}, TensorSpace{Tuple{Chebyshev{ChebyshevInterval{Float64}, Float64}, Chebyshev{ChebyshevInterval{Float64}, Float64}}, DomainSets.VcatDomain{2, Float64, (1, 1), Tuple{ChebyshevInterval{Float64}, ChebyshevInterval{Float64}}}, Float64}, TensorSpace{Tuple{Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}, Chebyshev{ChebyshevInterval{Float64}, Float64}}, DomainSets.VcatDomain{2, Float64, (1, 1), Tuple{ChebyshevInterval{Float64}, ChebyshevInterval{Float64}}}, Float64}, ApproxFunBase.CachedIterator{Tuple{Int64, Int64}, ApproxFunBase.Tensorizer{Tuple{FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}, FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}}}}, ApproxFunBase.CachedIterator{Tuple{Int64, Int64}, ApproxFunBase.Tensorizer{Tuple{FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}, FillArrays.Ones{Int64, 1, Tuple{InfiniteArrays.OneToInf{Int64}}}}}}, Float64}, TensorSpace{Tuple{Chebyshev{ChebyshevInterval{Float64}, Float64}, Chebyshev{ChebyshevInterval{Float64}, Float64}}, DomainSets.VcatDomain{2, Float64, (1, 1), Tuple{ChebyshevInterval{Float64}, ChebyshevInterval{Float64}}}, Float64}, Vector{Int64}, Float64}, b::Function)
   @ ApproxFunBase ~/.julia/packages/ApproxFunBase/BW4ev/src/Operators/general/algebra.jl:611
 [7] top-level scope

It works fine on Fun(X,[1.0,0]), so I figure this is a bug.

[dlfivefifty]

Fixed on ApproxFunBase#master, I'll tag now.