Revert ProductFun space promotion (#544)

* Revert ProductFun space promotion

* multiply KroneckerOperator with Fun

Author: jishnub

src/Multivariate/ProductFun.jl

@@ -109,10 +109,8 @@ true
 ```
 """
 function ProductFun(M::AbstractVector{VFun{S,T}}, dy::V) where {S<:UnivariateSpace,V<:UnivariateSpace,T<:Number}
-    sp = mapreduce(space, maxspace, M)
-    Msp = [Fun(f, sp) for f in M]
-    prodsp = sp ⊗ dy
-    ProductFun{S,V,typeof(prodsp),T}(Msp, prodsp)
+    prodsp = ProductSpace(map(space, M), dy)
+    ProductFun{S,V,typeof(prodsp),T}(copy(M), prodsp)
 end
 
 ## Adaptive construction

src/PDE/KroneckerOperator.jl

@@ -452,7 +452,16 @@ end
 function (*)(ko::KroneckerOperator{<:Operator, <:ConstantOperator}, pf::ProductFun)
     O1, O2 = ko.ops
     O12 = O2.λ * O1
-    ProductFun(map(x -> O12*x, pf.coefficients), factor(pf.space, 2))
+    vc = map(x -> O12*x, pf.coefficients)
+    if space(pf) isa TensorSpace
+        ProductFun(vc, space(vc[1]), factor(pf.space, 2))
+    else
+        ProductFun(vc, factor(pf.space, 2))
+    end
+end
+function (*)(ko::KroneckerOperator{<:Operator, <:ConstantOperator}, f::Fun{<:TensorSpace})
+    q = ko * ProductFun(f)
+    Fun(q)
 end
 
 function (*)(ko::KroneckerOperator, lrf::LowRankFun)