Avoid deadlock by closing pipe reader end

If we don't close this pipe reader with an error we ended up having a
deadlock as we keep trying to read indefinitely from it. This deadlock
causes the error message to be misguiding when attempting to upload a
layer with invalid format (gzip: invalid header).

Without this patch oc image append using an invalid layer format fails
with either "timeout" (docker.io) or "protocol error" (quay.io) instead
of reporting appropriate error ("invalid gzip").

pkg/helpers/image/dockerlayer/add/add.go

@@ -47,12 +47,14 @@ func DigestCopy(dst io.ReaderFrom, src io.Reader) (layerDigest, blobDigest diges
 	// calculate the diffID as the sha256 sum of the layer contents
 	pr, pw := io.Pipe()
 	layerhash := algo.Hash()
-	ch := make(chan error)
+	ch := make(chan error, 1)
 	go func() {
 		defer close(ch)
 		gr, err := gzip.NewReader(pr)
 		if err != nil {
-			ch <- fmt.Errorf("unable to create gzip reader layer upload: %v", err)
+			err := fmt.Errorf("unable to create gzip reader layer upload: %v", err)
+			pr.CloseWithError(err)
+			ch <- err
 			return
 		}
 		if !gr.Header.ModTime.IsZero() {