storage: workaround for an issue of vs2017

src/entt/entity/storage.hpp

@@ -477,7 +477,8 @@ private:
 
 /*! @copydoc storage */
 template<typename Entity, typename Type>
-class storage<Entity, Type, std::enable_if_t<ENTT_IS_EMPTY(Type)>>: public sparse_set<Entity> {
+// the useless decltype(...) helps to get around a quite impressive issue of VS2017
+class storage<Entity, Type, decltype(std::enable_if_t<ENTT_IS_EMPTY(Type)>())>: public sparse_set<Entity> {
     using underlying_type = sparse_set<Entity>;
 
 public: