registry: make ::valid backward compatible

src/entt/entity/registry.hpp

@@ -527,7 +527,7 @@ public:
      * @return True if the identifier is valid, false otherwise.
      */
     [[nodiscard]] bool valid(const entity_type entt) const {
-        return entities.contains(entt);
+        return entities.contains(entt) && (entities.index(entt) < entities.in_use());
     }
 
     /**

test/entt/entity/registry.cpp

@@ -576,8 +576,8 @@ TEST(Registry, CreateWithHint) {
     auto e2 = registry.create(entt::entity{3});
 
     ASSERT_EQ(e2, entt::entity{1});
-    ASSERT_TRUE(registry.valid(entt::entity{0}));
-    ASSERT_TRUE(registry.valid(entt::entity{2}));
+    ASSERT_FALSE(registry.valid(entt::entity{0}));
+    ASSERT_FALSE(registry.valid(entt::entity{2}));
     ASSERT_EQ(e3, entt::entity{3});
 
     registry.release(e2);

test/entt/entity/snapshot.cpp

@@ -270,7 +270,7 @@ TEST(BasicSnapshotLoader, GetEntityType) {
 
     ASSERT_TRUE(registry.valid(entities[0u]));
     ASSERT_TRUE(registry.valid(entities[1u]));
-    ASSERT_TRUE(registry.valid(entities[2u]));
+    ASSERT_FALSE(registry.valid(entities[2u]));
 
     ASSERT_EQ(storage.size(), 3u);
     ASSERT_EQ(storage.in_use(), 2u);