When a client reset handler fails because of an error in the callback, the SDK calls realm_register_user_code_callback_error to store it. However, the error that we in the callback provided to realm_sync_config_set_error_handler is realm_sync_error, which doesn't contain a pointer to the original error. So we get an error with a message A fatal error occurred during client reset: 'User-provided callback failed' and code 1028, but we don't have a way to get to the original error that caused the problem.

Note to self: to repro this in dart, throw a user exception in the client reset handler.