fix icon for nav items with on_top: true (#4487)
fix icon for nav items with on_top: true (#4487)

item.attribute('icon') is not defined, we need to call item.extra('icon').
Otherwise the icon will not be populated to the nav entry which is used together with the on_top-option
ARTACK/SonataAdminBundle,Soullivaneuh/SonataAdminBundle,peter-gribanov/SonataAdminBundle,UnDeleteRU/SonataAdminBundle,peter-gribanov/SonataAdminBundle,OskarStark/SonataAdminBundle,jordisala1991/SonataAdminBundle,jordisala1991/SonataAdminBundle,ARTACK/SonataAdminBundle,ossinkine/SonataAdminBundle,dmarkowicz/SonataAdminBundle,ossinkine/SonataAdminBundle,UnDeleteRU/SonataAdminBundle,jlamur/SonataAdminBundle,sonata-project/SonataAdminBundle,mweimerskirch/SonataAdminBundle,UnDeleteRU/SonataAdminBundle,greg0ire/SonataAdminBundle,osavchenko/SonataAdminBundle,dmarkowicz/SonataAdminBundle,osavchenko/SonataAdminBundle,ossinkine/SonataAdminBundle,osavchenko/SonataAdminBundle,greg0ire/SonataAdminBundle,mweimerskirch/SonataAdminBundle,jlamur/SonataAdminBundle,UnDeleteRU/SonataAdminBundle,OskarStark/SonataAdminBundle,jordisala1991/SonataAdminBundle,jlamur/SonataAdminBundle,UnDeleteRU/SonataAdminBundle,peter-gribanov/SonataAdminBundle,dmarkowicz/SonataAdminBundle,ARTACK/SonataAdminBundle,peter-gribanov/SonataAdminBundle,jlamur/SonataAdminBundle,Soullivaneuh/SonataAdminBundle,dmarkowicz/SonataAdminBundle,mweimerskirch/SonataAdminBundle,sonata-project/SonataAdminBundle,greg0ire/SonataAdminBundle,dmarkowicz/SonataAdminBundle,Armstrong1992/SonataAdminBundle,jordisala1991/SonataAdminBundle,OskarStark/SonataAdminBundle,OskarStark/SonataAdminBundle,Soullivaneuh/SonataAdminBundle,Armstrong1992/SonataAdminBundle,mweimerskirch/SonataAdminBundle,ARTACK/SonataAdminBundle,Soullivaneuh/SonataAdminBundle,jlamur/SonataAdminBundle,osavchenko/SonataAdminBundle,osavchenko/SonataAdminBundle,ossinkine/SonataAdminBundle,greg0ire/SonataAdminBundle