Fix error reporting in `CopyFileWithTar`

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
(cherry picked from commit 57e12037ac8f8eb48cc05979c3030853d011dfea)
Signed-off-by: Victor Vieux <vieux@docker.com>

pkg/archive/archive.go

@@ -1040,7 +1040,7 @@ func (archiver *Archiver) CopyFileWithTar(src, dst string) (err error) {
 		return nil
 	})
 	defer func() {
-		if er := <-errC; err != nil {
+		if er := <-errC; err == nil && er != nil {
 			err = er
 		}
 	}()