topojson - remove 'invalid' geometry type to avoid default constructed geometries

include/mapnik/json/topojson_utils.hpp

@@ -238,12 +238,6 @@ struct bounding_box_visitor
         }
         return bbox;
     }
-
-    box2d<double> operator() (mapnik::topojson::invalid const&) const
-    {
-        return box2d<double>();
-    }
-
 private:
     topology const& topo_;
     std::size_t num_arcs_;

include/mapnik/json/topology.hpp

@@ -86,10 +86,7 @@ struct multi_polygon
     boost::optional<properties> props;
 };
 
-struct invalid {};
-
-using geometry =  util::variant<invalid,
-                                point,
+using geometry =  util::variant<point,
                                 linestring,
                                 polygon,
                                 multi_point,

plugins/input/topojson/topojson_datasource.cpp

@@ -109,10 +109,6 @@ struct geometry_type_visitor
     {
         return static_cast<int>(mapnik::datasource_geometry_t::Polygon);
     }
-    int operator() (mapnik::topojson::invalid const&) const
-    {
-        return -1;
-    }
 };
 
 struct collect_attributes_visitor
@@ -121,8 +117,6 @@ struct collect_attributes_visitor
     collect_attributes_visitor(mapnik::layer_descriptor & desc):
       desc_(desc) {}
 
-    void operator() (mapnik::topojson::invalid const&) {}
-
     template <typename GeomType>
     void operator() (GeomType const& g)
     {