Blender Git Loki

BKE: bvhutils: Always return NULL when the BVHtree has no leafs.

BLI_bvhkdop functions were not made to work with zero-leaf trees.
Perhaps a better solution would be to modify BLI_bvhkdop to work with zero leaf trees.
But this solution of returning NULL was already used for bvhtrees of looptris.