Should fix the crashes reported in T69728
If I understand the code correctly we can only support on average 2 lines per vertex, Some might have less, other have more.
When assuming a mesh is triangulated the realistic average per vertex is 6 connected lines. So in the worst case we now only draw 2/3 of all the edges.
As an edge is only drawn once sculpt_vertex_count_get(ss) * 3 * 2 would be more realistic.