Qt4: drop window provider priority to zero
Qt4: drop window provider priority to zero

Mapping the Qt4 plugin requires a particularly long time and much
memory. So we had better avoid doing this everytime we create a new
video window (if the Qt4 interface is _not_ used).

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