Make `overapproximate` more robust

[alecarraro]

The function

LazySets.jl/src/Approximations/overapproximate.jl

Lines 364 to 371 in 458fb29

	function overapproximate(P::AbstractSparsePolynomialZonotope,
	::Type{<:UnionSetArray{Zonotope}};
	nsdiv=10, partition=nothing)
	q = nparams(P)
	dom = IA.IntervalBox(IA.interval(-1, 1), q)
	cells = IA.mince(dom, isnothing(partition) ? nsdiv : partition)
	return UnionSetArray([overapproximate(P, Zonotope, c) for c in cells])
	end

causes an error when the number of parameters of the SPZ is 0, since it is tries to create an interval box with 0 dimensions.