dense_set: handle conversion warnings

src/entt/container/dense_set.hpp

@@ -166,7 +166,7 @@ public:
           offset{other.offset} {}
 
     constexpr dense_set_local_iterator &operator++() noexcept {
-        return offset = it[offset].first, *this;
+        return offset = it[static_cast<typename It::difference_type>(offset)].first, *this;
     }
 
     constexpr dense_set_local_iterator operator++(int) noexcept {
@@ -175,7 +175,7 @@ public:
     }
 
     [[nodiscard]] constexpr pointer operator->() const noexcept {
-        return std::addressof(it[offset].second);
+        return std::addressof(it[static_cast<typename It::difference_type>(offset)].second);
     }
 
     [[nodiscard]] constexpr reference operator*() const noexcept {