Fix #127130: Snake Hook applies twist continually

Caused by d42aec3cf7

The prior cleanup missed setting the optionals into an invalid state
when the original code would set the `valid` flag to false.

Pull Request: https://projects.blender.org/blender/blender/pulls/127158

source/blender/editors/sculpt_paint/sculpt.cc

@@ -4548,6 +4548,8 @@ static void brush_delta_update(const Depsgraph &depsgraph,
   }
 
   /* Handle 'rake' */
+  cache->rake_rotation = std::nullopt;
+  cache->rake_rotation_symm = std::nullopt;
   invert_m4_m4(imat, ob.object_to_world().ptr());
   mul_mat3_m4_v3(imat, grab_location);