ui.backend.gtk: fix yield delay on gtk backend.
ui.backend.gtk: fix yield delay on gtk backend.

bpollack/factor,nicolas-p/factor,bpollack/factor,sarvex/factor-lang,AlexIljin/factor,AlexIljin/factor,dch/factor,nicolas-p/factor,dch/factor,dch/factor,factor/factor,tgunr/factor,tgunr/factor,tgunr/factor,dch/factor,bpollack/factor,nicolas-p/factor,sarvex/factor-lang,nicolas-p/factor,bjourne/factor,slavapestov/factor,dch/factor,slavapestov/factor,AlexIljin/factor,sarvex/factor-lang,slavapestov/factor,mrjbq7/factor,bjourne/factor,sarvex/factor-lang,AlexIljin/factor,factor/factor,slavapestov/factor,factor/factor,bjourne/factor,mrjbq7/factor,nicolas-p/factor,slavapestov/factor,mrjbq7/factor,factor/factor,mrjbq7/factor,sarvex/factor-lang,bjourne/factor,AlexIljin/factor,AlexIljin/factor,AlexIljin/factor,sarvex/factor-lang,slavapestov/factor,bjourne/factor,nicolas-p/factor,nicolas-p/factor,bpollack/factor,mrjbq7/factor,tgunr/factor,dch/factor,factor/factor,tgunr/factor,tgunr/factor,sarvex/factor-lang,bjourne/factor,bpollack/factor,bjourne/factor,slavapestov/factor,factor/factor,mrjbq7/factor,bpollack/factor,bpollack/factor