gh-37106: Additive identity of EllipticCurve should always be minimum
This is inspired by how `.automorphisms()` always return the identity
morphism as the first automorphism. So now `min(E.points()) == 0` always
holds (when `E.points()` is nonempty and finite).
#sd123 🚀
URL: https://github.com/sagemath/sage/pull/37106
Reported by: grhkm21
Reviewer(s): grhkm21, Lorenz Panny