Init the scene of the draw context when selecting. When using face dot selection on when the subsurf modifier is active on the cage, the scene needs to be valid. It is read from the context in the `DRW_mesh_batch_cache_create_requested` and used in the `isDisabled` method of the SubSurfModifier. Reviewers: fclem, sergey Differential Revision: https://developer.blender.org/D5214