image: Fix dangling image detection with graphdrivers

The isDangling function was incorrectly identifying images as dangling
when they had no RepoTags but had valid RepoDigests.

This can occur when the graphdrivers are used instead of the containerd
image store.

An image should only be considered dangling if it has no RepoTags,
regardless of whether it has RepoDigests.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

Author: vvoland

cli/command/image/list.go

@@ -177,7 +177,7 @@ func shouldUseTree(options imagesOptions) (bool, error) {
 
 // isDangling is a copy of [formatter.isDangling].
 func isDangling(img image.Summary) bool {
-	if len(img.RepoTags) == 0 && len(img.RepoDigests) == 0 {
+	if len(img.RepoTags) == 0 {
 		return true
 	}
 	return len(img.RepoTags) == 1 && img.RepoTags[0] == "<none>:<none>" && len(img.RepoDigests) == 1 && img.RepoDigests[0] == "<none>@<none>"