0030146: Visualization - exception during attempt to display Edge without geometry

StdPrs_ToolRFace no skips curves with NULL curves.
Code has been cleaned up from duplicated checks, redundant casts
and dummy Adaptor2d_Curve2dPtr typedef.

StdSelect_BRepSelectionTool::GetSensitiveForFace() now catches
Standard_NullObject exception to skip invalid Edges.

src/BRepAdaptor/BRepAdaptor_Curve.hxx

@@ -86,7 +86,10 @@ public:
   //! is  raised if  the edge does  not have a pcurve on
   //! the face.
   Standard_EXPORT BRepAdaptor_Curve(const TopoDS_Edge& E, const TopoDS_Face& F);
-  
+
+  //! Reset currently loaded curve (undone Load()).
+  Standard_EXPORT void Reset();
+
   //! Sets  the Curve <me>  to acces to the  geometry of
   //! edge <E>.
   Standard_EXPORT void Initialize (const TopoDS_Edge& E);