[Gtk] Fix CreateMultiSizeIcon for single size images
[Gtk] Fix CreateMultiSizeIcon for single size images

residuum/xwt,akrisiun/xwt,cra0zy/xwt,hamekoz/xwt,mono/xwt,hwthomas/xwt,antmicro/xwt,lytico/xwt,TheBrainTech/xwt