ui.backend.gtk: add auto-position for worlds with { 0 0 } in window-loc
ui.backend.gtk: add auto-position for worlds with { 0 0 } in window-loc

mcandre/factor,erg/factor,erg/factor,erg/factor,erg/factor,erg/factor,mcandre/factor,mcandre/factor,mcandre/factor,erg/factor,mcandre/factor,erg/factor,mcandre/factor,mcandre/factor