import: Raise error if the imported image is filtered out

During import, if an image does not match the host's platform,
it won't have any children labels set, which will result in the
Garbage Collector deleting its content later, resulting in an
unusable image. In this case, we should fail early.

This can still be bypassed by using ctr import --all-platforms.

Signed-off-by: Claudiu Belu <cbelu@cloudbasesolutions.com>

import.go

@@ -185,7 +185,7 @@ func (c *Client) Import(ctx context.Context, reader io.Reader, opts ...ImportOpt
 
 	handler = images.FilterPlatforms(handler, platformMatcher)
 	handler = images.SetChildrenLabels(cs, handler)
-	if err := images.Walk(ctx, handler, index); err != nil {
+	if err := images.WalkNotEmpty(ctx, handler, index); err != nil {
 		return nil, err
 	}