Handle empty coeff vectors in Multiplication for Ultraspherical spaces

[jishnub]

On master

julia> v1 = Fun(Chebyshev(), Float64[])
(::Fun{Chebyshev{ChebyshevInterval{Float64}, Float64}, Float64, Vector{Float64}}) (generic function with 1 method)

julia> sp = Ultraspherical(1)
Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}(1, -1.0..1.0 (Chebyshev))

julia> Multiplication(v1, sp)
ERROR: BoundsError: attempt to access 0-element Vector{Float64} at index [1]
Stacktrace:
 [1] getindex
   @ ./array.jl:861 [inlined]
 [2] SymToeplitzOperator(V::Vector{Float64})
   @ ApproxFunBase ~/.julia/packages/ApproxFunBase/fvVRN/src/Operators/banded/ToeplitzOperator.jl:25
 [3] Multiplication(f::Fun{Chebyshev{ChebyshevInterval{Float64}, Float64}, Float64, Vector{Float64}}, sp::Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64})
   @ ApproxFunOrthogonalPolynomials ~/Dropbox/PostDoc/RossbyWaves/RossbyWaveSpectrum.jl/dev/ApproxFunOrthogonalPolynomials/src/Spaces/Ultraspherical/UltrasphericalOperators.jl:33
 [4] top-level scope
   @ REPL[14]:1

This PR

julia> Multiplication(v1, sp)
ApproxFunBase.MultiplicationWrapper{Chebyshev{ChebyshevInterval{Float64}, Float64}, Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}, ApproxFunBase.SpaceOperator{HankelOperator{Float64}, Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}, Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}, Float64}, Float64}(Fun{Chebyshev{ChebyshevInterval{Float64}, Float64}, Float64, Vector{Float64}}(Chebyshev{ChebyshevInterval{Float64}, Float64}(-1.0..1.0 (Chebyshev)), Float64[]), ApproxFunBase.SpaceOperator{HankelOperator{Float64}, Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}, Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}, Float64}(HankelOperator{Float64}(Float64[]), Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}(1, -1.0..1.0 (Chebyshev)), Ultraspherical{Int64, ChebyshevInterval{Float64}, Float64}(1, -1.0..1.0 (Chebyshev))))

julia> Multiplication(v1, sp)[1:4, 1:4]
4×4 BandedMatrix{Float64} with bandwidths (0, 0):
 0.0   ⋅    ⋅    ⋅ 
  ⋅   0.0   ⋅    ⋅ 
  ⋅    ⋅   0.0   ⋅ 
  ⋅    ⋅    ⋅   0.0

[codecov]

Codecov Report

Merging #70 (dc62f3c) into master (17583d6) will not change coverage.
The diff coverage is n/a.

❗ Current head dc62f3c differs from pull request most recent head b93a8fd. Consider uploading reports for the commit b93a8fd to get more accurate results

@@           Coverage Diff           @@
##           master      #70   +/-   ##
=======================================
  Coverage   57.04%   57.04%           
=======================================
  Files          27       27           
  Lines        2386     2386           
=======================================
  Hits         1361     1361           
  Misses       1025     1025           

Impacted Files	Coverage Δ
...c/Spaces/Ultraspherical/UltrasphericalOperators.jl	75.92% <ø> (ø)

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[dlfivefifty]

Bump the patch version if you want this tagged