Inconsistency with FastTransforms.jl

[Sheehan Olver]

n = 600
    S = KoornwinderTriangle(0.0,-0.5,-0.5)
    ff = (xy) -> P(18,8,0.,-0.5,-0.5,xy...)
    p = points(S,n)
    v = ff.(p)
    PP = plan_transform(S,v)
    v̂ = PP.duffyplan*v
    F = tridevec_trans(v̂)
    F̌ = FastTransforms.cheb2tri(F,0.,-0.5,-0.5)
    F̌₂ = PP.tri2cheb \ F
    norm(F̌ - F̌₂)
size(F)
F̃ = copy(F)
c_cheb2tri(c_plan_tri2cheb(size(F,1),0.0,-0.5,-0.5),F̃)

[Mikael Slevinsky]

This can be distilled to an error using execute_tri_hi2lo_AVX512 with an odd number of columns.