Bug fix trace test fails for witness sets with real linear subspace

[PBrdng]

This fixes #726

[PBrdng]

@oskarhenriksson ?

[oskarhenriksson]

Looks like a very elegant fix to me! Maybe there should be a regression test for this, e.g., by adding

@test trace_test(W_L) < 1e-8

after line 23 here:

HomotopyContinuation.jl/test/witness_set_test.jl

Lines 3 to 24 in 0a86032

	@testset "affine" begin
	@var x y
	F = System([x^2 + y^2 - 5], [x, y])
	W = witness_set(F)
	@test dim(W) == 1
	@test codim(W) == 1
	@test degree(W) == 2
	@test solutions(W) isa Vector{Vector{ComplexF64}}
	@test results(W) isa Vector{PathResult}
	L = LinearSubspace([1 1], [-1])
	W_L = witness_set(W, L)
	@test degree(W_L) == 2
	@test sort(real.(solutions(W_L))) ≈ [[-2, 1], [1, -2]]
	@test linear_subspace(W_L) == L
	@test trace_test(W) < 1e-8
	end