runc list: fix error reporting for non-existent root

The idea of commit d1fca8e was right (report errors for non-existent
root, unless using the default root dir) but the logic was inverted.

Fix the logic.

Test case for default root requires non-existent /root/runc, which is
not always possible.

Reported-by: RedMakeUp <girafeeblue@gmail.com>
Co-authored-by: RedMakeUp <girafeeblue@gmail.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

list.go

@@ -119,7 +119,7 @@ func getContainers(cmd *cli.Command) ([]containerState, error) {
 	root := cmd.String("root")
 	list, err := os.ReadDir(root)
 	if err != nil {
-		if errors.Is(err, os.ErrNotExist) && cmd.IsSet("root") {
+		if errors.Is(err, os.ErrNotExist) && !cmd.IsSet("root") {
 			// Ignore non-existing default root directory
 			// (no containers created yet).
 			return nil, nil