QuadPointEvaluator not initializing properly

[MelanieInky]

When using multiple domains, QuadPointEvaluator is initialized for all domains even if we pass only one of the domain to it. The code

`
using FerriteAssembly
using Ferrite

struct DummyMat end
m = DummyMat()

grid = generate_grid(Quadrilateral,(2,2))
addcellset!(grid,"p1",Set([1,2]))
addcellset!(grid,"p2",Set([3,4]))

dim = 2
ip = Lagrange{RefQuadrilateral,1}()^dim
cellvalues = CellValues(QuadratureRule{RefQuadrilateral}(2), ip);
dh = DofHandler(grid)
add!(dh, :u, ip)
close!(dh);

domains = Dict(
"p1" => DomainSpec(dh,m,cellvalues;set = getcellset(grid,"p1")),
"p2" => DomainSpec(dh,m,cellvalues;set = getcellset(grid,"p2")))

buffer = setup_domainbuffers(domains)

qp_eval =QuadPointEvaluator{Float64}(buffer["p1"],Returns(1.0))
#This initialize the evaluation
println(qp_eval.data)
`
Produces the output:

julia> qp_eval.data
4-element Ferrite.CollectionsOfViews.ArrayOfVectorViews{Float64, 1}:
[6.9515042965956e-310, 6.9515042965972e-310, 6.95150429659876e-310, 6.95150428459415e-310]
[6.95150428446293e-310, 6.951501998935e-310, 6.95150429655923e-310, 6.9515042967189e-310]
[6.95150429660666e-310, 6.95150429661615e-310, 6.95150429661773e-310, 6.9515042966193e-310]
[6.9515042966209e-310, 6.95150429662247e-310, 6.9515042940913e-310, 5.7524e-320]

[KnutAM]

FerriteAssembly.jl/src/Workers/QuadPointEvaluator.jl

Lines 48 to 57 in 70e2d38

	nqps = Vector{Int}(undef, ncells)
	nqp_total = 0
	for (_, db) in domainbuffers
	cv = get_values(get_base(get_itembuffer(db)))
	@assert cv isa CellValues # For now, only CellValues supported
	nqp = getnquadpoints(cv)
	set = getset(db)
	map(i -> (nqps[i] = nqp), set)
	nqp_total += nqp * length(set)
	end

Looks like we need something like

- nqps = Vector{Int}(undef, ncells)
+ nqps = zeros(Int, ncells)
- nqp_total = 0
for (_, db) in domainbuffers 
    cv = get_values(get_base(get_itembuffer(db))) 
    @assert cv isa CellValues # For now, only CellValues supported 
    nqp = getnquadpoints(cv) 
    set = getset(db) 
    map(i -> (nqps[i] = nqp), set) 
-   nqp_total += nqp * length(set) 
end
+ nqp_total = sum(nqps)

and redirect the case with a single domain to a dict with a single entry. This should also make it compatible with having one cell part of multiple domains if desired.