registry: handle conversion warnings

src/entt/entity/registry.hpp

@@ -539,7 +539,7 @@ public:
      */
     version_type destroy(const entity_type entt) {
         for(size_type pos = pools.size(); pos != 0u; --pos) {
-            pools.begin()[pos - 1u].second->remove(entt);
+            pools.begin()[static_cast<typename pool_container_type::difference_type>(pos - 1u)].second->remove(entt);
         }
 
         entities.erase(entt);