A user-supplied window handle (external_view) becomes the superView
of internal_view, which is closed with [view removeFromSuperview].
This fails silently if external_view = NULL (no handle supplied).
Call [win_internal_id close] in this case. Fixes#4432.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9049>