The code responsible for culling back faces in cloud geometry is not exactly right. Since the fast-mode rendering does not use back-face culling, it incorrectly culls the bottom most faces and causes a crash due to the geometry buffer being empty.

We should fix this by skipping the face-cull logic when using fast-mode rendering. If the geometry buffer is empty after the meshing step, don't attempt to finalize it into a GPU vertex buffer.

I might look into this if nobody else has their eyes on it already