Stackoverflow with QR

[Kolaru]

Using j′vp on a QR factorization result in a stackoverflow, like in the following example:

using FiniteDifferences
using LinearAlgebra

X = randn(5, 5)
j′vp(central_fdm(5, 1), X->qr(X).Q, randn(5, 5), X)

I believe it is due to the fact that vec(Q) return a Base.ReshapedArray (for Q, R = qr(X)).

Causes problem while testing JuliaDiff/ChainRules.jl#306