Qt: no need to iterate two times. always disable empty menus
Qt: no need to iterate two times. always disable empty menus

Note: in some rare case when p_aout != NULL but the audio
      ouput is "empty" (no track), then the visualizations
      are still enabled (but of course, you can't use them).

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