factor.el: fix for empty strings font lock.
factor.el: fix for empty strings font lock.

bjourne/factor,factor/factor,slavapestov/factor,bpollack/factor,factor/factor,mcandre/factor,mcandre/factor,nicolas-p/factor,erg/factor,Keyholder/factor,mcandre/factor,bpollack/factor,erg/factor,slavapestov/factor,slavapestov/factor,factor/factor,tgunr/factor,mcandre/factor,nicolas-p/factor,factor/factor,mrjbq7/factor,AlexIljin/factor,littledan/Factor,ehird/factor,erg/factor,kingcons/factor,bpollack/factor,dch/factor,seckar/factor,erg/factor,ceninan/factor,mrjbq7/factor,bjourne/factor,bjourne/factor,littledan/Factor,erg/factor,factor/factor,slavapestov/factor,bjourne/factor,mrjbq7/factor,dch/factor,cataska/factor,AlexIljin/factor,tgunr/factor,erg/factor,sarvex/factor-lang,kingcons/factor,tgunr/factor,kingcons/factor,dharmatech/factor,dch/factor,tgunr/factor,cataska/factor,nicolas-p/factor,bpollack/factor,dch/factor,nicolas-p/factor,seckar/factor,bpollack/factor,tgunr/factor,bpollack/factor,slavapestov/factor,AlexIljin/factor,ceninan/factor,tgunr/factor,Keyholder/factor,mcandre/factor,dch/factor,nicolas-p/factor,cataska/factor,bjourne/factor,ceninan/factor,sarvex/factor-lang,mcandre/factor,mrjbq7/factor,AlexIljin/factor,sarvex/factor-lang,littledan/Factor,sarvex/factor-lang,sarvex/factor-lang,jwmerrill/factor,dch/factor,mcandre/factor,AlexIljin/factor,mrjbq7/factor,AlexIljin/factor,bjourne/factor,dharmatech/factor,seckar/factor,erg/factor,jwmerrill/factor,bjourne/factor,slavapestov/factor,mrjbq7/factor,ceninan/factor,cataska/factor,AlexIljin/factor,bpollack/factor,factor/factor,ehird/factor,nicolas-p/factor,jwmerrill/factor,slavapestov/factor,sarvex/factor-lang,littledan/Factor,ehird/factor,kingcons/factor,dharmatech/factor,Keyholder/factor,nicolas-p/factor,sarvex/factor-lang