view: stable single type view ::find function

src/entt/entity/view.hpp

@@ -763,7 +763,7 @@ public:
      * iterator otherwise.
      */
     [[nodiscard]] iterator find(const entity_type entt) const noexcept {
-        return view->find(entt);
+        return view ? view->find(entt) : iterator{};
     }
 
     /**

test/entt/entity/view.cpp

@@ -79,6 +79,7 @@ TEST(SingleComponentView, InvalidView) {
     ASSERT_EQ(view.size(), 0u);
     ASSERT_TRUE(view.empty());
     ASSERT_FALSE(view.contains(entt::null));
+    ASSERT_EQ(view.find(entt::null), view.end());
 
     ASSERT_EQ(view.front(), static_cast<entt::entity>(entt::null));
     ASSERT_EQ(view.back(), static_cast<entt::entity>(entt::null));