Support vector of Ball2 in zero direction

[schillic]

Currently:

LazySets.jl/src/Sets/Ball2.jl

Line 128 in 62decef

If the direction has norm zero, the origin is returned.

This is wrong because the call should always return an element of the set. The following example shows why this behavior is needed:

julia> X = CartesianProduct(Ball2([1.0], 0.5), Ball2([1.0], 0.5));

julia> σ([1.0, 0], X)
2-element Vector{Float64}:
 1.5
 0.0

julia> σ([1.0, 0], X) ∈ X
false