SDLPP: make copySelf actually copy everything

sdlpp/sdlpp_rectcolider.cpp

@@ -88,4 +88,9 @@ SDL_Rect RectColider::getRect() {
         r.h = pixel_h;
     return r;
 }
+
+std::shared_ptr< CollisionPolygon > RectColider::copySelf() {
+    return std::make_shared< RectColider >( *this );
+}
+
 } // namespace SDLPP