ui.backend.gtk: simplify <window-handle>.
ui.backend.gtk: simplify <window-handle>.

mrjbq7/factor,factor/factor,factor/factor,bjourne/factor,bpollack/factor,bjourne/factor,tgunr/factor,mrjbq7/factor,AlexIljin/factor,bjourne/factor,bjourne/factor,bpollack/factor,nicolas-p/factor,nicolas-p/factor,bpollack/factor,bpollack/factor,mrjbq7/factor,AlexIljin/factor,bpollack/factor,mrjbq7/factor,factor/factor,nicolas-p/factor,bpollack/factor,bjourne/factor,mrjbq7/factor,factor/factor,tgunr/factor,AlexIljin/factor,tgunr/factor,bpollack/factor,AlexIljin/factor,bjourne/factor,tgunr/factor,factor/factor,nicolas-p/factor,factor/factor,nicolas-p/factor,AlexIljin/factor,tgunr/factor,AlexIljin/factor,AlexIljin/factor,nicolas-p/factor,mrjbq7/factor,bjourne/factor,nicolas-p/factor,tgunr/factor