Check for empty vectors before trying to access a pointer to the first element in Octree<T, use_pairs, AL>::cull_convex().
Check for empty vectors before trying to access a pointer to the first
element in Octree<T, use_pairs, AL>::cull_convex().

(cherry picked from commit 54c36adbec05a8e120f8e962a324eed4fc8e22ed)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot