`irfft` not supported for `PaddedView` but `rfft` is

[PaddedView](https://github.com/JuliaArrays/PaddedViews.jl) arrays are partly supported

```julia
using AbstractFFTs
using PaddedViews

shortsamp = cos.(0:256 * pi / 16);
paddedsamp = PaddedView(0.0f0, shortsamp, (512,))
fftshortsamp = rfft(shortsamp);
fftpaddedsamp = rfft(paddedsamp); # RFFT of padded array OK
paddedfftshortsamp = PaddedView(0.0f0, fftshortsamp, (257,)) ;
irfft(fftpaddedsamp, 512);
irfft(paddedfftshortsamp, 512); ## IRFFT of padded array not OK
```
results in an error at the last line

```
MethodError: no method matching plan_brfft(::PaddedView{Complex{Float64},1,Tuple{Base.OneTo{Int64}},Array{Complex{Float64},1}}, ::Int64, ::UnitRange{Int64})
Closest candidates are:
plan_brfft(!Matched::Union{DenseArray{Complex{Float32},N}, ReinterpretArray{Complex{Float32},N,S,A} where S where A<:Union{SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray}, ReshapedArray{Complex{Float32},N,A,MI} where MI<:Tuple{Vararg{SignedMultiplicativeInverse{Int64},N} where N} where A<:Union{ReinterpretArray{T,N,S,A} where S where A<:Union{SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray} where N where T, SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray}, SubArray{Complex{Float32},N,A,I,L} where L where I<:Tuple{Vararg{Union{Int64, AbstractRange{Int64}, AbstractCartesianIndex},N} where N} where A<:Union{ReinterpretArray{T,N,S,A} where S where A<:Union{SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray} where N where T, ReshapedArray{T,N,A,MI} where MI<:Tuple{Vararg{SignedMultiplicativeInverse{Int64},N} where N} where A<:Union{ReinterpretArray{T,N,S,A} where S where A<:Union{SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray} where N where T, SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray} where N where T, DenseArray}}, ::Integer, ::Any; flags, timelimit) where N at /home/dan/.julia/packages/FFTW/2okGQ/src/fft.jl:678
plan_brfft(!Matched::Union{DenseArray{Complex{Float64},N}, ReinterpretArray{Complex{Float64},N,S,A} where S where A<:Union{SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray}, ReshapedArray{Complex{Float64},N,A,MI} where MI<:Tuple{Vararg{SignedMultiplicativeInverse{Int64},N} where N} where A<:Union{ReinterpretArray{T,N,S,A} where S where A<:Union{SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray} where N where T, SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray}, SubArray{Complex{Float64},N,A,I,L} where L where I<:Tuple{Vararg{Union{Int64, AbstractRange{Int64}, AbstractCartesianIndex},N} where N} where A<:Union{ReinterpretArray{T,N,S,A} where S where A<:Union{SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray} where N where T, ReshapedArray{T,N,A,MI} where MI<:Tuple{Vararg{SignedMultiplicativeInverse{Int64},N} where N} where A<:Union{ReinterpretArray{T,N,S,A} where S where A<:Union{SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray} where N where T, SubArray{T,N,A,I,true} where I<:Union{Tuple{Vararg{Real,N} where N}, Tuple{AbstractUnitRange,Vararg{Any,N} where N}} where A<:DenseArray where N where T, DenseArray} where N where T, DenseArray}}, ::Integer, ::Any; flags, timelimit) where N at /home/dan/.julia/packages/FFTW/2okGQ/src/fft.jl:678
plan_brfft(::AbstractArray, ::Integer; kws...) at /home/dan/.julia/packages/AbstractFFTs/PUqOK/src/definitions.jl:285

Stacktrace:
[1] #plan_irfft#19(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::Function, ::PaddedView{Complex{Float64},1,Tuple{Base.OneTo{Int64}},Array{Complex{Float64},1}}, ::Int64, ::UnitRange{Int64}) at /home/dan/.julia/packages/AbstractFFTs/PUqOK/src/definitions.jl:334
[2] plan_irfft(::PaddedView{Complex{Float64},1,Tuple{Base.OneTo{Int64}},Array{Complex{Float64},1}}, ::Int64, ::UnitRange{Int64}) at /home/dan/.julia/packages/AbstractFFTs/PUqOK/src/definitions.jl:334
[3] #plan_irfft#18(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::Function, ::PaddedView{Complex{Float64},1,Tuple{Base.OneTo{Int64}},Array{Complex{Float64},1}}, ::Int64) at /home/dan/.julia/packages/AbstractFFTs/PUqOK/src/definitions.jl:285
[4] plan_irfft(::PaddedView{Complex{Float64},1,Tuple{Base.OneTo{Int64}},Array{Complex{Float64},1}}, ::Int64) at /home/dan/.julia/packages/AbstractFFTs/PUqOK/src/definitions.jl:285
[5] irfft(::PaddedView{Complex{Float64},1,Tuple{Base.OneTo{Int64}},Array{Complex{Float64},1}}, ::Int64) at /home/dan/.julia/packages/AbstractFFTs/PUqOK/src/definitions.jl:283
[6] top-level scope at In[62]:10
```

It seems like if we do the RFFT we should also also be able to invert it. Perhaps it's as simple as extending that union type. I can prepare a patch for this but want to check in whether that is sane first.