skins2: fix corner case with old skins and fullscreen
skins2: fix corner case with old skins and fullscreen

For skins without video elements, fullscreen mode could be launched with the inner video kept hidden. Initializing the video control to NULL fixes it.

shyamalschandra/vlc,krichter722/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,vlc-mirror/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,xkfz007/vlc,shyamalschandra/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,krichter722/vlc,krichter722/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,krichter722/vlc,krichter722/vlc,shyamalschandra/vlc,vlc-mirror/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,xkfz007/vlc,shyamalschandra/vlc,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc,krichter722/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,vlc-mirror/vlc