Fix: Crash when toggling dynamic topology off

Before some recent refactors, normals were always calculated
when creating the sculpt BVH tree. Switching from dyntopo BMesh
back to base mesh sculpting, that didn't happen anymore.
Nowadays it makes more sense to update the normals as necessary
where they are used, so the intent of the code that uses normals
is clearer.

Pull Request: https://projects.blender.org/blender/blender/pulls/127111

source/blender/editors/sculpt_paint/sculpt.cc

@@ -5036,6 +5036,8 @@ bool SCULPT_cursor_geometry_info_update(bContext *C,
     return true;
   }
 
+  bke::pbvh::update_normals(*depsgraph, ob, *ss.pbvh);
+
   /* Calculate the sampled normal. */
   if (const std::optional<float3> sampled_normal = calc_area_normal(
           *depsgraph, brush, ob, node_mask))