[GTK] Canvas issue drawing fix
[GTK] Canvas issue drawing fix

Adjust the drawing origin only when the canvas is not using its
own GdkWindow.

antmicro/xwt,steffenWi/xwt,TheBrainTech/xwt,iainx/xwt,akrisiun/xwt,hwthomas/xwt,cra0zy/xwt,sevoku/xwt,residuum/xwt,mono/xwt,mminns/xwt,lytico/xwt,mminns/xwt,hamekoz/xwt,directhex/xwt