default the schema version to 0 when a schema is provided

src/js_realm.hpp

@@ -351,6 +351,9 @@ void RealmClass<T>::constructor(ContextType ctx, ObjectType this_object, size_t
             if (!Value::is_undefined(ctx, version_value)) {
                 config.schema_version = Value::validated_to_number(ctx, version_value, "schemaVersion");
             }
+            else if (schema_updated) {
+                config.schema_version = 0;
+            }
 
             static const String migration_string = "migration";
             ValueType migration_value = Object::get_property(ctx, object, migration_string);