Some of the media player interfaces don't use the given
SystemChildWindow, but they work with the parent window handle.
e.g. directx (avmedia/source/win) and
quicktime (avmedia/source/quicktime)
Without the parent window handle they create a
separate child window outside impress window.
It affects only editing and not the slideshow.

Change-Id: I80252ce35fcd29ab2cce081299529b85129017ee