BACKPORT: layer/layer_store: ensure NewInputTarStream resources are released

Upstream reference:
moby@d147fe0
Fixes BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1661443

Signed-off-by: Sergio Lopez <slp@redhat.com>

Author: slp

layer/layer_store.go

@@ -222,13 +222,14 @@ func (ls *layerStore) applyTar(tx MetadataTransaction, ts io.Reader, parent stri
 	}
 
 	applySize, err := ls.driver.ApplyDiff(layer.cacheID, parent, rdr)
+	// discard trailing data but ensure metadata is picked up to reconstruct stream
+	// unconditionally call io.Copy here before checking err to ensure the resources
+	// allocated by NewInputTarStream above are always released
+	io.Copy(ioutil.Discard, rdr) // ignore error as reader may be closed
 	if err != nil {
 		return err
 	}
 
-	// Discard trailing data but ensure metadata is picked up to reconstruct stream
-	io.Copy(ioutil.Discard, rdr) // ignore error as reader may be closed
-
 	layer.size = applySize
 	layer.diffID = DiffID(digester.Digest())