tty-child-frames support makes the undecorated set to nil even on graphic frame

[kiennq]

The new change of

                       ;; NOTE: TTY child frame use undecorated to control border.
                       (undecorated . ,(not (and (> border-width 0)
                                                 (featurep 'tty-child-frames))))

makes the example show as decorated frame (with title bar and everything) instead of just a child frame even in the graphic frame