Blender Git Loki

Dyntopo: Delete OpenGL buffers of nodes that do not have any more
triangles.

It is possible to end up with such nodes using brushes in aggressive
collapse mode. Those nodes should normally be cleaned up, since they can
never be actually reused (adding more geometry to a node requires the
node having some geometry to begin with) but until we support dynamic
nodes, better delete those to avoid binding graphics driver resources.

If such zero elements buffers were used, GL error out of memory would be
reported.