internal/pkg: close gzip reader on success

The Close method panics otherwise.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/tar.go

@@ -97,12 +97,11 @@ func (a *tarArtifact) Cure(t *TContext) (err error) {
 	}
 
 	defer func(f io.ReadCloser) {
-		closeErr := tr.Close()
 		if err == nil {
-			err = closeErr
+			err = tr.Close()
 		}
 
-		closeErr = f.Close()
+		closeErr := f.Close()
 		if err == nil {
 			err = closeErr
 		}