Entire push skips WAL if there's a validation error in any of its samples

If I understand correctly, when using chunk-storage, if a single sample fails validation during ingestion (ie, due to out-of-order or duplicate timestamp), then none of the samples in the request will make it to the WAL either, even though some may have been added to the chunk: https://github.com/cortexproject/cortex/blob/master/pkg/ingester/ingester.go#L435
