Speed up IndexSet::count() a bit
Speed up IndexSet::count() a bit

realm/realm-object-store,realm/realm-object-store,realm/realm-core,realm/realm-js,realm/realm-js,realm/realm-core,realm/realm-js,realm/realm-core,realm/realm-js,realm/realm-js,realm/realm-js,realm/realm-object-store,realm/realm-core,realm/realm-js,realm/realm-core,realm/realm-js,realm/realm-core,realm/realm-core,realm/realm-js