Fix right tangent calculation.
Fix right tangent calculation.

If we find a point that's the same as the reference, we will return the next
one. I didn't prove this is mathematically correct, but by intuition I'd say
that if the tangent is the reference itself, then the next one works as well.

stefanozanella/mpi_convex_hull,stefanozanella/mpi_convex_hull