Blender Git Loki

Fix T88658: Force Fields of curve shape can crash if curve has only one point

`bvhtree_from_mesh_edges_create_tree` can actually leave the BVHTree
NULL (e.g. if no edges are present).

Now dont allocate `BVHTreeFromMesh` on the `SurfaceModifierData` at all
in case the tree would be NULL anyways.
Places like `get_effector_data` check for `SurfaceModifierData`-
>`BVHTreeFromMesh` and dont try to stuff like getting a closest point on
surface, which would crash as soon as BVHNodes would need to be accessed
(from the NULL BVHTree).

Maniphest Tasks: T88658

Differential Revision: https://developer.blender.org/D11443